More power for moderate listening levels?

The answer to this is complicated.

Can you give us more specifics about your speaker, your amp and listening room?

Do the 2' test.  Sit 2 ' from your speaker and ask if it still sounds strained, if not, it's the room.

Thanks for the quick response.
Pass Labs Int-25 driving Harbeth Shl5+.
Speakers are about 7' apart and about 3'out from the short wall of a 14' x 24' room. 9' ceilings.
My listening chair is 8-9 ft away and this is where I listen most. In this position, instruments are clearly defined in the soundstage and I'm really happy with tone, clarity, and quite frankly the oomph of this little amp.  Occasionally, we will have "dance parties" with the kids and we turn it up and this is when I notice a difference in clarity. At this point, we are much further away and the room could very well be in play. I do not however, listen at these levels in my chair. 
I've been told by a few folks at Pass that the Int-250 would definitely "drive" my Harbeths better. I'm not sure what this means and I remain skeptical. Hence the question: If I sat in my chair where the acoustics are great and I swapped amplifiers while listening at medium levels, would the bigger Pass make a difference? Let's forget about other differences like the 250 being a balanced design. WDYT?

It doesn't work that way, and we don't need to know anything about your room. Geez Louise! This is because amps and power don't work anything like the way the vast majority thinks they do. Its perfectly possible you could find a lower power amp that sounds hugely better at both low and high volume. Class A has nothing to do with it either. These kinds of generalities sound all logical and certain but they break down real fast the minute you hook up the exception to the rule.  

You don't mention the power of your Class A amp. But that doesn't matter either. Unless its like single digits. Because once you get up around 20-50 watts then its not the amp. Its the speakers. If yours are low sensitivity (92dB/1w/1m) then it very quickly becomes almost impossible to find an amp powerful enough to play them loud. Particularly if they are below 90, then you can pretty well forget about it. This is why you see all these guys searching around for the right amp. Its not the amp. Its the speakers.

LOL!!! I was writing while you were writing. First thing I checked, your speakers are hopelessly inefficient. Harbeth has the hutzpah to say they are easy to drive! Not at 86dB they're not! Doesn't matter the impedance! Now you know why you see all these guys in love with their speakers searching searching searching for the amp. Its not the amp. Its the speakers. 

Also notice I didn't need any details. I worked this all out simply based on your first post.

Thanks for the responses. 
The assumption is that the lower powered amplifier drives the speakers just fine at moderate listening levels. My listening says yes.
At the SAME volume, will a higher powered amp improve the sound quality?

OP  That WAS your question (In your second post). I fail to see any progress towards an answer being made by yammerng about "it "

brianbiehs OP6 posts11-03-2020 10:51am
"...."At the SAME volume, will a higher powered amp improve the sound quality?"

Always nice to have extra power (headroom) on tap to handle the dynamics and the INT-250 @ 250wpc would certainly do the job, as Pass indicated. The INT-25 @ 25wpc, however, is Class A vs INT-250's Class A/B, and the sound quality at moderate power levels may be better on the smaller amp. The only way to find out is to A/B the two in your system.

turnbowm 

Thanks for answering my question 

There have been several threads of late on amps to drive Harbeths.  Short summary: there is no easy answer.  Take a look.  That being said, you would probably have been better off with the 30.8 for a bit more oomph.

Hello brianbiehs,

     You didn't mention which main speakers you're utilizing but, based on your user profile thread participation details, it seems like you're using Harbeth super HL5+ main speakers.  If this is correct, these are very high quality 6 ohm speakers that are 86 db/@ 1 watt/1 meter efficient with no large impedance dips, which a low powered class A amp should have no problem driving to moderate volume levels. 
     I just read a 6 Moons review of your speakers, linked to below, in which the reviewer was very impressed by these speakers, stating "the Super works well with tube, solid-state class A/B or class D amplification, whether it puts out 8 or 800 watts".  

http://6moons.com/audioreviews2/harbeth/1.html

     If the reviewer can drive your speakers well using an 8 wpc Coincident Dynamo SET tube amp, it suggests to me that your issue may be better explained by a poor preamp to amp impedance match rather than just your amp.
    Exactly which brand and model preamp and amp are you using?  For optimum performance, the rated input impedance of your amp should ideally be about 10X the rated output impedance of your preamp.
     I suggest you start by gathering the facts on your gear, you can either do it yourself or give me the details on your amp and preamp brand/models and I could check it out for you.

 Tim       

Thanks for the replies and Tim, thanks for the offer. My amp is an integrated so no preamp issues here. sorry for the confusion, I'm not reporting a problem so much as wondering whether there could be an improvement on already good sound. Many folks pair their Harbeths with lower power amps and yes, good results can be had. An amp with significantly more power than my Int-25 would certainly drive my speakers to higher volumes with less distortion depending on the amp. Another way to ask the question is: Is this the only benefit?

Aside from helping the dynamic range as turnbown suggested, are there any other attributes associated with extra power in reserve that would augment medium level listening?

@noble100 I would appreciate the offer of you helping me to know whether I am paired correctly and what I need to look for in a pre amp when I go that route. I have a Sunfire Cinema Grand V rated at 200wpc, my integrated is a Denon AVRX3500H. It has 5 pre outs so I am able to harness all 5 channels. Of course only 2.1 when listening to music. Speakers are Polk RTiA7s. I'm looking at a future upgrade in both speaker and pre amp. Thank you!

This is not an easy question to answer, and it would depend on particulars that are impossible to factor in, such as your own personal preferences and priorities.  My own priority is for the amp to sound good while playing at lower output levels where the vast majority of my listening takes place.  For me personally, I happen to favor the sound of low-powered triode tubes, and even in the solid state realm, the amps I like tend to be lower-powered, such as the gear from First Watt.  This means using fairly efficient speakers (mine are 99 db/w efficient).

Millercarbon raised a very point--lower efficiency speakers cannot really achieve good dynamics no matter how much power is fed because of thermal compression.  As more power is fed to the voice coil, it heats up and that heating increases resistance which reduces the amount of power that can be delivered to the driver.  The less efficient the speaker, the greater the compression.  My difference with his opinion is that I would not be so dismissive of the Harbeths just because they are not efficient; there are plenty of other reasons to like any particular speaker even if it cannot do "really loud."

It might be the case that the higher powered Pass amp will improve the sound, even at lower levels of play, but, I have my doubts about this because caused by some inherent superiority of having much more power in reserve.  This is something you will have to try for yourself to see if it is the case.  A long time ago, I auditioned an am rated to deliver something like 50 watts/channel.  The same company made a 200 watt/channel amp that the dealer said was very similar in design and parts quality, but used more output devices to achieve the higher power capability.  I actually preferred the sound of the lower powered amp in a direct comparison.

Can you be more specific when you say you hear strain or lack of clarity at higher volume levels — maybe give some specific examples?

I agree that auditioning is the only way to go to see if one amp is better sounding than the other. Just curious about the effect of power at lower volumes.

At high volume I think the amp is staining because horns and cymbals are becoming harsh and not as musical. Overall, music is just not as pleasant and I gather it's not just due to high volume irritating my ears.

Appreciate the thoughts y'all.

How loud are you listening?  If you're trying to do 110dB, then there are better loudspeakers than the Harbeths.  Also, you mention that you're further away from the loudspeaker and dancing (presumably standing), both of which will alter the tonal balance of the loudspeaker.  Do the Harbeths sound strained at your normal listening position at high volume levels?

What is the volume level setting when you crank it up and notice the strain?  The XA-25 (same amp used in the INT-25) was tested by Stereophile at 80Wpc into 8 ohms and 130Wpc into 4 ohms. It does switch to class A/B at higher power output levels, so perhaps you are hearing that change?
I'm using the Pass INT-25 with Sonus Faber Electa Amator III speakers, 87db, 4 ohm, probably a more difficult speaker to drive than your Harbeths.  With my chair at about 8 feet from the speakers I usually set the volume in the range of 40 to 50 depending on the CD (63 is the max volume). I've also wondered if a higher power amp might drive these speakers better, although I don't think I'd want to give up the INT-25 for moderate listening levels.

There is nothing inherent in the design of an amp which will mean a higher powered amp will sound less good at low volumes than a low powered amp. The Pass Labs Int 250 may sound better or worse at low volume to your ears through your Harbeths than the 25. Whichever, it won’t be because of the amp wattage that there is a difference.  Whereas at high volume the amp output obviously is a defining factor. 

Great questions and comments.

Do the Harbeths sound strained at your normal listening position at high volume levels? 
This is a test I need to critically evaluate. 

What is the volume level setting when you crank it up and notice the strain?
Definitely can't get well into the 50's. Volume level in the 40's is still sweet and musical.

I think a big takeaway from this discussion is that sometimes you don't mess with a good thing.

At the SAME volume, will a higher powered amp improve the sound quality?

No. It does not work that way. As the great Robert Harley said, "If the first watt isn’t any good, why would you want 200 more of them?" Good question. You have a great amp. You have great speakers. Unfortunately way too inefficient to sound good together at anything more than medium volume.

What nobody seems to want to admit, at 86dB you need 2 watts just to get to 89 dB. Doesn’t sound like much. No problem, you got 25. But remember, that’s measured at 1m. Do you sit at 1m? Not even. Sound disperses at a somewhat different rate for different speakers but the inverse square is a good first approximation. That is to say, twice as far away, 2 squared is 4, you get 1/4 the volume. Let’s say you sit real close, just 2m away. Now you need 2 watts just to get back to 86, which is not very loud. To play 89 you need 4 watts. At 92 dB its 8w. 95, now just barely getting to what someone might consider loud, you need 16, and your amp is just about tapped out. 105 is plenty loud, but 10dB calls for ten times the power, or 160 watts.

These are the most conservative possible numbers. Sit even a little further back, in a normal room with normal absorption, and using average volume not intermittent peaks, you can easily wind up with ten times that, and there are not a lot of 1,600 watt amps. Which to me sounds about right for playing those speakers at satisfyingly loud volume. No wonder your beautiful Pass is strained.

A huge amount of our perception of "strain" is tied into volume. With seriously inefficient speakers such as these its just real hard to get the mind around the fact all that power is going into.... not much. Just wasted. Not even going into heat. The speakers can handle much more. Its just a bad design, for anything other than moderate volume listening.

Which, remember again, first thing I said, you have great speakers and a great amp. Just not great if you want to listen at high volume. Horses for courses.

I don't think you need more power, but you may need different power.

As a counter point, if you can listen to Ayre, Bryston and Luxman you should.

86 db sensitivity 25 wpc amp? LOL Do you have a buddy with Parasound, A21,23.  Something like that. Krell 100 or 250 wpc, Mark L will push those puppies.. If you want a pitch black background, some type of class d. They are 1/3 the cost of the Pass but 25 X the power.

Not only will they power your speakers, you can see for yourself, without all the bluster about less efficient speakers. BLA BLA BLA...

NOT twice as much 25 times as much..... BUY a bigger amp..

25 watts per channel is 25 watts per channel

If you you want to one up that, Treat as much of the room as you can stand.  I like as little room treatment as possible.

Those are great sounding speakers, with accurate factory measurements.  86 is just fine with todays amps that are from 2-2000 watts, EASY 2-3-4000 WPC not uncommon. No need to scrimp..

So were are clear, I own Pass, First Watt, and two kits I built... and at least 3 pairs of speakers that are 84%.. They can sound up
50 X 50 X 15 dance floor to over 100 db... CLEARLY... Zero floor noise zip nada..... That's with an old vinyl rig too (Russco) and a C20 Mac.

25 wpc? At least it's a good 25 watts... NOW 250 or better...

Regards

Hello,
I agree with so many of you it is hard to keep track. I have had the exact same issues all corrected by the things said in this thread. 200 watt class A to crank up the volume. A used pass 250, you are talking some serious money. I have tried the Ayre, Mark Levenson, Hegel. It’s not the amp it’s the speakers. You can pull 45,000 pounds of freight with a semi-tractor/trailer but only go about 75 Mph or pull practically nothing in a Porsche and go 200 mph plus. To get something to cover it all it’s tough and very expensive. That’s why Porsche doesn’t make semi trucks and Mack doesn’t make sports cars. 
 It’s very simple. For the dance parties get a different pair of speakers like very efficient Klipsch RP-600m maybe with a separate amp. You need a very efficient speaker with a horn or horns in it. Maybe upgrade to the Cornwall. A lot of people put them on the wall so they can be out of the way or maybe on a completely different wall. I say leave your nice sounding system alone and create a second system. You might be able to get away with a BlueNode Powernode 2i $899 with the Klipsch RP-600m on sale now for $450. All the home theater guys love Klipsch speakers and ported SVS subs for home theater because they play loud very well. Everyone who watches a movie in my theater says it’s the best sounding home theater they have been in. That’s because my system is setup for quality not quantity. It will play loud enough for it to be a little uncomfortable which I don’t do.  This can be a rabbit hole you don’t get out of and can be very expensive. Better to avoid the rabbit hole all together. Concert speakers are not audiofile speakers. They consist of an array of horns with humongous bass drivers. If you need the bass to go with your face party add an inexpensive ported sub. 

In my opinion the most overlooked spec when choosing an amp is the reserve amps or instantaneous amps. This is a power reserve that helps especially in the midrange and lower end. It will also improve dynamics and overall sound at all levels. This is a simplified explanation but I don't want to right a whole book here.

Here's the thing.. That  Mack and that Porsche both have close to the same horsepower, and torque.. Look them up you'll see. 2-500 hp with
1-2000 foot lbs of torque..  The difference is the size of the parts..... 
Foot lb of torque... BIGGER

Same thing with speakers, it's where the speaker starts to distort not how efficient it is. The E factor is rather arbitrary, IF the distortion is LOW and reproduction is correct, Audiofile or not.... That is my end of the line goal.

If I can reproduce quality sound from 40db to 115db, I'm a pretty happy soul.  I don't use my ears either.  I've found if you don't run sound test, and collect your own data, your wasting your time..

When I mentioned the 84% speakers, the factory was 89 or 91.. THEY aren't usually accurate, and it's REAL easy to fudge the measurements.

Bigger amp, treat the room... You want to make sure to run some test and see if its running out of gas, and distorting... Pass is not the end all amp it's made out to be.. It is a great amp though.. I like Ampzilla, Serious amp, there. Hook a single 2000, up.. You'll see.. Compare the two..
Wish I would have never sold them...:-( You could have turn them up until your ears bleed, with those speakers... 25 watts is 25 watts plane and simple.

Regards

Brian, I think you answered your own question. If you are straining at times you either need more power, more efficient speakers or add subwoofers and a 2 way crossover. 
I am of the camp that there is no such thing as too much power. XA100.8s would be the minimum IMHO. For that money I would get JC1+'s. Good high powered amps have an effortlessness missing in smaller amps(unless you have very efficient speakers.) Before you notice the harshness the amp is already clipping on transients "stressing the sound."  I tend to go for speakers on the less efficient side, 89dB or so and would never consider an amp less than 200 watts. I also have a tendency to gravitate towards class A amplifiers and I also use subwoofers crossed at 125dB which increases the headroom of my system 10 dB. With all this I can get 110 dB out of ESLs. More than enough to give you a headache. 
With your system I would (and this is me) get a Trinnov Amethyst preamp, XA 100.8's and at least two passive subs. With the Harbeths this would give you a SOTA point source system for sure which should do an easy 105 dB probably more. It would be totally effortless at lower levels and for sure put a big smile on your face whenever you light it up.

Mike

What you are looking for is more of what the XA25 delivers, power and great sound. 

Much to sort through here. I thought the thread might die after a few posts but the community here really came through. Thanks all. 

I owned the Harbeth SHL5+ for many years and they sound great at moderate volume as well as loud volume. I bought the Harbeth's because I sold my house and they played well at lower volumes unlike the Vandersteen Quatro's I had before.

I successfully used an Ayre AX-7e in combination with an Ayre Codex and in my 15 x 21 x 9 room I could not crank the volume loud enough to cause any distortion. The Ayre is only 60 watts and still drove the SHL5+ well. I upgraded to the Aesthetix Mimas integrated, which puts out 150 watts a channel, and that was even better. So I am not sure that more power is the answer you are looking for. Alan Shaw says that any 100 watt+ amp should work on any of his speakers. I would suggest trying a few different amps to see what works best with the Harbeth's in your room.

I did try the Pass 250.5 amplifier along with the Audio Research LS26 preamp and I did not like it with the Harbeth's. Nothing against Pass, just not my cup of tea. Sounded great with my Quatro's though.

Good Luck!

Using an SPL calculator you should be able to achieve 97 to 100dB levels at your normal listening position.  The Pass amp is rated at 50 watts peak power.  Personal taste differ and some would not consider this level very loud.  I suggest you use an SPL meter to gauge how loud you listen and at what point your system starts to sound strained.

It’s an experiment that I want to try. Also, just using my ears to Identify acceptable listening levels at my chair. Could save the strain on my amp as well as my wallet!

As more power is fed to the voice coil, it heats up and that heating increases resistance which reduces the amount of power that can be delivered to the driver. The less efficient the speaker, the greater the compression.

Horsefeathers. Very efficient speakers have wimpy motors that may not control the cone as well as a less efficient speaker. The voice coil has to get to ≈90°C for a 1db reduction. While voice coil heating effect is measurable, it is difficult to detect. Our ears begin self-preservation clamping at elevated levels, which some may interpret as voice coil heating compression.

see http://www.ielogical.com/Audio/WinterBlues.php#TheFly for a bit on voice coil heating.

@brianbiehs:
Install an app like AudioTool on your phone and get some real measurements as to the levels you are reaching.

25wpc at 2.6m [8.5ft] max out @ 95db PEAK on 86dB/W/m speakers. At 5m [16.5ft] max level is 89db. Add room noise from a bunch of people and the apparent level will be somewhat lower.

Be aware that changing amplifiers to support Disco may severely compromise audio quality at less taxed listening levels.

More speakers are blown by party levels than almost all other causes combined.

There is no free lunch!

1- Do you like the speakers ?
2-Don't listen to the B.S
3-You need more power for those higher listening levels, Get it !
4-Lot's out there, volumes of B.S. out there as well, you'll just have to wade through.

That Pass is a good amp but only 25 w/ch.

WHat you are hearing is most likely the amp clipping, ie struggling to deliver the power needed at higher volume to those not very efficient but very good sounding Harbeth speakers (if driven to the max properly)..

You need more power to go louder and clearer. It’s that simple. Basic physics and hifi 101.

Along with more power, more current delivery capability can again only help. From what I read, that is likely the case with those Harbeth. You need a better quality amp with higher quality power supply for that.

Higher damping factor specs and ability to double power into 4 ohms is a good indicator of a beefy amp capable of delivering lots of current when needed.

That is what you need to play it safe.

What amp specifically? Harder to say. A good quality Class D amp 200 w/ch into 8ohm, 400 into 4 or more would be a good bet. 100 w/ch to 8 ohm, 200 to 4 might even cut it.

It all depends how loud you need to go. Clipping is public enemy # 1. YOu want to avoid that at all costs. Power and current is your insurance policy for that. 25w/ch won’t cut it with most speakers out there for higher SPLs that are loud and clear.

TUbe amps are popular choices with Harbeth and can sound very good, but a higher power tube amp capable of driving Harbeth to their max at higher volume could cost some serious $$$$s and will consume a lot of power whenever on, whereas Class D is a reasonable alternative that should lower cost and keep power bills down.

Most tube amps and Class D amps soft rather than hard clip, so that will make it seem like fewer watts can go furtherbut will limit absolute SPLs and dynamic range. Still more digestible kind of distortion  to the ear than hard clipping. ANother reason tube amps and Class D are both reasonable choices depending.

As long as you can avoid clipping as described, specific amp choice will matter less. They all will be up to the task. Can’t sound good if not up to the task......not as hard if so.

If you enjoy the Pass sound I would certainly step up to a 250.8 you will still be getting the first 18 watts in class A where most of your listening is and plenty of reserve for loud listening. I have one powering my Maggie 3.7 and never hear any straining.

It really comes down to priorities and preferences. If high quality at high volume is a priority then you need different speakers. Its that simple. The power demands of those speakers at high volume, forget reserve, you need hundreds of watts. Need. To use. Not have in reserve. Whatever that even means. 

Tekton makes some great speakers, very high efficiency, great sound, and their favorite amp is Pass. It would seem a match made in heaven.  

But if on the other hand you're totally in love with the medium volume sound, able to understand what's going on and live with the compromise at higher levels, that's fine too. 

Most of what I see here though sounds like trying to have it both ways. Since horses for courses didn't gain any traction how about don't put legs on a snake? You have some fine speakers, for what they are. Don't try and make them what they're not. Doing something up a rope, or into the wind, comes to mind.

Cheapest solution is to bi-amp using 200+ wpc of class D for the bass
speaker.
Use the Pass 25 on the upper only. 

Also borrow/buy someone's measuring equipment to see if and when the clipping occurs.

Then report back.

If you want to go louder and clearer you can change amps and go for more muscle or change speakers to something that is better suited to 25 watts.  But they won't be Harbeths.

I found myself in a similar situation. I drive Sonus Faber Sonettos II with Pathos Classic One MKIII. Although I'm very pleased how it sounds at moderate to loud listening levels, every time I crank the volume up I feel like I miss dynamics and grunt from the amplifier. It seems the amplifier is having a hard time driving the speakers when reaching 85db+ SPL at my listening spot which is no more than 9 feet from the speakers. 
I'm on the same crossway as you. I really like the sound of the pathos but I always feel I need more power for the speakers to shine ...

Tekton makes some great speakers

IF one likes that sort of thing.

In the Monitor review, Stereophile determined "My estimate of the Impact's sensitivity was 87.5dB(B)/2.83V/m, considerably lower than the specified 94dB." https://www.stereophile.com/content/tekton-design-impact-monitor-loudspeaker-measurements

Truth in advertising: Miller owns Tektons.

If I measured them they would be different again. As I said, I've seen a LOT of fudging and manipulation, of the numbers. How that mic is held what it is held with, background noise, I've seen some weird stuff to get NUMBERS. Wiring out of phase is real big.  Listen to the difference, when the mids are NOT wired out of phase... and when just one of three (EX; mid drivers) is wired out of phase, the number look good but  they sound "FLAT" because they are, they measure flat...

Tekton does not wire out of phase.... I don't know Mr. Pass views on  crossovers, but I do have one of his hand built First Watt  OXO.  Nothing more than 18 db XO, more like 6 and 12 db.. His amps are going to reflect sounding better, with a lower order XO, too.. Those long slopes help a lot when it comes to power demand...and lower watts.

24, 48 db slopes, and any low watt amp, the amp will labor, AND run out of gas.  Even if the E factor is high.... 25 watts is 25 watts..I have to look up the specs on the speakers...I have a hunch about the crossover...I just wonder if it is in the specs without, looking at the actual crossover.

Regards..

More power allows you to hear more of the instruments at lower volumes (e.g. sound floor).

I have Martin Logan Spires which are nominally 4Ω, but can draw down to 1Ω on some loads. Yeah, they've been known to blow up underpowered amps.

I drive them with a pair of 900 W monoblocks (4Ω), fed by a tubed (6SN7) preamp. I also have tube monoblocks that put out 75 W. 

When listening with the tube amps, the sound floor doesn't reach as low as with the s/s amps.

Klipsch makes wonderful-sounding, efficient speakers.
My thought is keep the current Pass, get different speakers.
Not an owner (I prefer Vandersteens).
Just my 2c...

All,

As MC stated, it's coming down to personal preference.I really like the sound of the Harbeth/Pass combination. I realize it's not everyone's cup of tea and I do have limited experience. However, I can listen for hours on this system while following precise bass lines and subtleties I did not know existed. Cliche I know.
Given all the great comments, I think the path to audio nirvana is a simple one for me:
1) Sit in the chair and critically listen at highish volumes (without risking speaker damage of course). Do I achieve sufficient loudness without losing clarity and oomph? Case closed.  
2) Sit there and wish for more? Go with more sensitive speakers (doubtful) or get a higher powered amp. If going this route it makes sense to me to skip an animal in the food chain and try the Int-250 with an increase from 95db to 105db at my listening chair. Looking at the distortion/watt graph, the 25 clips at 60W so I'm giving myself a ballpark of about 50W. Someone correct me if I'm wrong, but pushing it to 50W may be a problem if there is a big dynamic range in the music. The 250 deserves an audition but it comes at a steep (for me) price. It may be worth it, it may not.

And again, thanks for all the comments and suggestions. I'm seeing that the journey is part of the fun.

I have Super HL5 Plus and am currently running them with a 50 WPC tube integrated (ARC VSI55).  They are in my office, so I don't typically crank them up, but with the volume halfway up they are very dynamic and sound great.  At the low level I usually listen, they sound wonderful.  They're not going to fill a large room with sound though with 50 watts and I can't imagine they'd be satisfying with a 25 WPC amp if you want to listen loud from time to time. 

I have used them in my main system with 180 WPC tubed monoblocks and they can go to ear damaging levels, however I think they lose a little finesse. 

One of my friends had 40.2s with a Line Magnetic LM-805iA 48 WPC tube integrated and it was one of the best systems I've heard.  I didn't hear them cranked, but the detail, dynamics, micro dynamics, imaging, soundstage... it was all there. 

A little more quantity wouldn't hurt, but I'd focus more on quality than getting the most watts you can.  That is, assuming you decide you're not satisfied with the levels your current amp can drive the speakers to.

I hadn’t thought of TWO amps!

"You can never have too much power"--probably attributed to Bob Carver, inventor of the Phase Linear 500 and 700.  Sure, they blew-up a lot, but when they worked, they were shrill and loud.

Bi-amp with an external x-over or get two identical amps that will run in mono.

OR, buy a big honkin' solid state amp and rock out, I guess.

Speakers have to match amps in efficiency vs output to be ideal.

 Your dealer should have pointed this mismatch out to you given your desire for occasional high-volume listening.  Has he/she been to your room and listened to what he/she sold you?

Get a better dealer.

Cheers!

I have heard, and liked, the HL5+, and to me, even with lower-powered tube amps, it can play quite loudly.  But, my idea of loud might be different from yours.  In building any speaker, compromises must be made, and I doubt that the HL5+ was designed to have extreme volume level as a strength.  The distortion you thought had been creeping in as the volume got louder might be something in the speaker and not necessarily a problem with the  amplifier you were using.  It would be instructive if you can find a more powerful amp to compare with the one you are using now.

I would personally be more inclined to be looking at amps that sound better at the volume levels I normally listen at, even if it means sacrificing some performance when playing at extremely high volume.  This is how I ended up with three tube amps, the one with the highest power rating being 6.5 watts/channel.