Benchmark AHB2 compared to Rogue Atlas Magnum III

Very different amps indeed, and I’m sure your excellent speakers will easily reveal the differences.  It completely depends on what improvements/sound characteristics you’re after.  What amp are you using now?  The Rogue will add a little — though not too much — tube warmth and tonal color/richness whereas the Benchmark will give you a similar sonic signature of your DAC, that being very detailed and neutral.  Your call.

It's not just a matter of the speaker being good enough to reveal differences. It will have a lot to do with the impedance of the speaker at various frequencies, causing the tube amp to produce a slightly different frequency response. A good speaker with stable impedance will sound more similar between the two. A good speaker with bigger peaks and dips in impedance will be more revealing of their differences.

The only way to know for sure if you'll like one better than the other with your F208s is to give them both a try. 

Absolutely they will sound different largely due to output impedance difference as per @asctim and the difference in distortion. The only way to know which you prefer is to listen and compare.

Difference is between virtually no distortion and able to drive anything, vs the often preferred distortions, not well quantified, from tube amplifiers. 

Just my impression, but tubes seem to be more dynamic for the power. Amps like the Benchmark somehow seem a bit stiff upper lip if you get what I mean. Could be I am so used to MOSFET amps. 

Another impression, the metal domes in Revel's ( listened to bookshelf's only) just get to me slightly from otherwise very well balanced speakers. Guess I am just a soft dome guy. ( leaning to either my own or Sonas Faber) 

Only way to make the choice is compare them both side by side. Listening one by one does not tell you much. Our memory is not that good and out subconscious bias is stronger. You will hear what you want to hear and it does not matter what you think you want to hear. 

IMHO, there is no such thing as a good speaker with stable impedance.  Some better than others, some horrible, and yes it effects the sound of an amplifier.  The better the amp, the more load invariant it will be.  I expect the Benchmark to be immune, where a Fosi V3 is a disaster.  Really ugly impedance/phase can actually cause an amp to be unstable if the feedback compensation was not well enough done. Boy to I know about his. $$

As I have improved my speakers, DACs, amps, I am in a quandary. Really good recordings sound better, but poor ones sound worse. Makes me wonder if the distortions and masking of tubes, maybe preamp, would help the overall musicality. Most of my music is "my generation" so early remasters of tape or first generation digital, so not very good. 

@tvrgeek

My impression of these really well controlled, ultra low distortion amps is similar to yours. Stiff upper lipped is a great description. I’ve used the word "dry" in an attempt at a description of the effect, but they seem to have an iron fist on the speaker, minimizing its ability to express some character in its relationship to the amp. I’m sure it’s technically correct. I do like that sound in some ways but I think I’d need to design a speaker and setup a room around that as a starting point. The upside potential I’d bet is ultimately higher.

No really good speakers with stable impedance? Can you elaborate on that further?

And yes! There is a struggle between perfection that brings out the best in the best recordings vs. a forgiving sloppiness that doesn’t fully reveal the best but is graceful with less than the best. What to do? It’d be nice if you could just flip a switch or turn a knob on your system to go from exacting to more forgiving. With my active crossovers and EQ I can sort of do that. I’ve found that a really flat and extended response sounds great with some good recordings, but on most stuff sounds too edgy and bright. I need more downward slope in the treble to get a forgiving but less airy and spacious sound. Also a tighter directivity with less room reflection is fantastic on some recordings, where others need some room reverb to soften, blur and sort of fatten up the sound. I think there’s more to it than just bad and good recordings, but different kind of recordings needing a different playback to sound their best.

About metal domes, I don’t have a clear opinion on it due to a lack of much experience, but so far my favorite speakers that didn’t use compression drivers had soft dome tweeters. What always amazes me about a soft dome doped silk tweeter is that it can make such detailed, shimmery metallic sounds when they’re in the recording. It’s hard to get my mind around how a slightly rubbery, tacky, soft thing can sound like that.

On the speaker impedance: Speakers are horribly complex loads. Unfortunately, most amps are tested with resistive loads.  Flat response into 8 Ohms etc. Well speakers have resonance peaks, phase shifts, dips or peaks due to the crossover and rising with frequency.  Typically.  Good designers can minimize these to some extent. Now a well designed amplifier is a VOLTAGE amplifier and should care not what the load does. It should supply whatever current is needed for the voltage gain.  2 to 30 Ohms from 1/4W to full power, 20 to 20K  is a fair range. One clue is if the power @ 4W is double that of 8 and they claim 2 Ohm stable.  Usually this is a function of power supply and feedback implementation.  Poor class D amps seem to have great difficulty with this.  Newer ones, just fine. ( I still don't seem to like them though). Solid State can do this. Tubes are tougher as the transformer would like to see a narrower impedance  range as a load. Probably why synergy with tubes is a litter harder than with SS. This issue is not a mystery and can be measured but it is not a single number to be advertised. 

Mastering is a problem.  Billy Joel recordings seem to have 4100 really boosted. Loudness wars peaking to 0 dB which really screws up digital filters. Moody Blues were just plain terrible. Early Beatles really hard Left and Right, not stereo.  Sheffield mastered very low level for wider dynamic range. The only thing I can think of is to evaluate and pre-process every track in the digital domain and store the processed results for playback. 

Trying to get used to my new Schiit Vidar. Quite clean. Not quite Benchmark, but clean. Different from my MOSFET ( my own). Seems to do drum impacts cleaner but less dynamic.  Better control so keeps the drivers from flopping in the breeze?  Am I used to a sloppy sound?  I converted my mains to sealed from ported at the same time, so a difference there. ( I prefer low Q sealed alignments) My main focus is on female vocals and possible sibilance, then if solo instruments sound right. Guitar, obo, flute. I gave up on pianos as I don't think one has ever been recorded well. 

Listened to a lot of speakers recently up to about 5K. Of all of them I find I liked the Sonas Faber Lumina''s the best but at medium volume. They can't really do a Beethoven crescendo.  Revels were very well balanced, but just can't take the hard dome. Not much else I liked at all. I tried a couple hard domes in my speakers (Seas ER18 paper woofers, and a series of domes and crossovers)  Back to the SB soft dome.  I was hoping the AMT's would advance now the patents expired, but nope, every one I heard is terrible. Air with a big helping of distortion to go with it. 

The end result is that is is still up to the individual. Hearing is our brains interpretation of the sound. It is not real. We all have our sensitivities and preferences so "right" is only in the eyes ( ears) or the individual.  I can't tell you what you will hear. I may know a power cord can't by the laws of physics make a difference in "air" , but that does not mean people who believe they do are making it up when they hear it. They hear it, real or not.  Our brains are the biggest liars on the planet. 

PS: I have heard soft domes break up and sizzle worse than a $2 aluminum one. So, like everything else, "it depends"  I just have not heard a metal dome I liked including the new Be uber-priced ones. I would say it is the tweeter, not the crossover as I have tried to tame several SEAS metal domes, got fine free-field response, but not liked them. 

I sold my AHB2 to raise cash to buy an amp for my Magnepan LRS+, a Magtech. That was a great move, but I do miss the sound of the AHB2 with an appropriate matching speaker.

I have a speaker in my Livingroom that the AHB2 would work well with, the Yamaha NS5000. I have a CODA #16 on it now and it blows me away each time I listen. However, I still feel the AHB2 is the best amp I have heard on the top end. With a slightly warm speaker it will be amazing. The plan is to get a second amp for the NS5000 to switch around. The CODA is overall better but the AHB2 is so unique, sound wise. I have a Benchmark LA4 preamp with the NS5000 system.

The tweeters on my NS5000 are made of Zylon as is the mid and 12-inch woofer.

The Energy 2.8 Veritas ( made in ‘94) were made with a complex crossover intended to minimize impedance changes.

They were made with the option for passive Triamping but the manual explicitly says not to use external crossovers and bypass the internal crossover.

They use special house made aluminum mids/tweeters and I have yet to hear anyone say anything bad about them- engineering/design is more important to the sound than the choice of material .

I’ve owned both these amplifiers. I also own a pair of F208s currently.

Unfortunately, I cannot tell you which is definitely the best match because I didn’t own all these items at the same time.

The Benchmark is a vastly quieter amp, for which reason I would be inclined to choose it for the fairly sensitive Revels. It can also reach deeper in the bass, though its midbass output is not as robust as the Rogue’s. The Benchmark is dead neutral with an even-keeled presentation. The Rogue OTOH, is very midrange-forward with most speakers—a more “first row” presentation compared to the typical 4th/5th row presentation of most amplifiers.

With a little patience and a little more money than the AHB2, you can get a pre-owned Coda No.8 which is significantly better than either the Rogue or the Benchmark. The Yamaha A-S2100 also has great synergy with the F208s and IMO is a better amp than the Rogue in most regards.