Listening Levels for Classical Music / Slightly electronic sound at high levels

Try a 500 watt a side rated for 2 ohms and it will go away .

This is probably wrong but I think not impossible. What you hear might be your Pass transistors' artifacts that were masked by less resolving speakers. In my analog based solid state system I don't hear what you described, but there is always something that annoys me to a degree and I know what it is - transistors, this kind of slightly metallic/electronic/recessed sound signature.

At this point, playing vinyl may be the way to diagnose this issue. Most modern pressings originate from digital production/mastering which does impart different characteristics than AAA.
   My advice; use a known high quality record from either an analogue or digital master to test your speakers. You can check reviews of vinyl you own, or buy a high quality analogue recording. There are so many available.

I don't know much about digital but I did hear an opinion that many people underestimated the importance of digital cables. Just a thought. 

Thanks inna, that has actually occurred to me but of course just about every recording these days is made digitally. Because of my extraordinary lazy nature I have grown use to listening to nothing but digital files mostly high resolution streamed to the PS Audio DAC. I DO have a VPI rig for vinyl but even alot of vinyl is derived from digital recordings. I also think of the Thiels as high resolution speakers but perhaps the Personas are high resolution as "under an electron microscope" and that’s what I’m hearing. My VPI table, when I use it, feeds the Aesthetix Janus which I have but which is presently out of the loop in favor of the Calypso (its the same unit without the phono stage). So YES I’ve been thinking all day about switching out the Calypso with the Janus and listening to vinyl and seeing what that yields.

Here is my hypothesis, and I am sorry if I am right. What you hear with your very high resolution speakers are digital artifacts, something that you could not hear with your Thiel speakers. Whether they come from the recording, from your dac, from digital cable or all of them is another question.
It does not sound to me like amp/speakers mismatch.
What folkfreak said also could be, at least to partly contribute.
If you have any analog source, try with it.

Good point lowrider, the source of my digital files in a NAS located one floor down from my listening room, said files being delivered via ethernet into the Bridge II on the back of the PS Audio DAC.  I do have small vibration control cushions I don't know what they're called but they're little multilayered pucks that are sold in some tweak vendors for lots of money but available from Parts Express I think cheap.  The only think that I have "real" audiophile vibration control on is the outboard motor unit on my VPI Scoutmaster table (some Symposium things purported to be very high tech).  So I could probably improve on that which no doubt would tighten things up but I really do think I'm hearing a difference in the way the speakers present the information on the recording.

Are you using any vibration control or isolation on your sources? You have a PSA dac, what is your source?
I’m asking since the highs with orchestral music on my system resulted in a sizzle or digititis. I changed DACs and added a reclocker to lower jitter, but the harshness remained. Then I took measures to control vibration from my components. Treating my PSA transport was a step in the right direction. Next was my DAC, and the playback was now sounding like music with realistic highs. Brass instruments will always have a raspy quality, that’s their nature.
The components will vibrate on their own and in my case, there was an acoustical issue from a woofer directed at my audio rack.
I recommend addressing jitter and vibration if you haven’t already.

Vandersteen, Magico, Thiel (as is in other Thiels such as the 3.7 which, with two large bass drivers should be perhaps better capable for properly reproducing orchestral peaks without compression.

I know the amp is not running out of steam, far from it, the needle on the Pass 150.8 doesn't move even at the loudest playback levels.  Its only driving on each side one midrange and one tweeter (the speakers have powered subs).  I think there's a sense in which the Personas are more highly resolving than the Thiels but the Thiels are a bit more forward in the midrange, are less electronic sounding which seems to me to involve the speaker reproduces the sound around the solo instruments.  Its a difficult thing to put into words, what I'm hearing that is.  Of course that is the nature of the beast.  And Yes that's the argument against the Personas, that for that much money I should be able to "have it all."  Today I've been running convolution in room with filters derived in REW that bring the top end down a tiny bit which makes louder levels seem more realistic and less electronic so I suppose it could just be a question of that slight tilt up in the response of the Persona speakers.  Fortunately I have the most patient dealer rep in the world as I labor over this decision.  I'm beginning to think its going to be harder than just auditioning a few different speakers available to me here in Atlanta, that rather it might be a good idea to start attending a few shows like the APOXNA show coming up in Chicago, before I sink money into what will, at 61, be my "last" speaker.  Of course another audiophile friend asked me if such a thing exists.  YES.  At least for me, that's what I'm after.  

I just looked at the specs. I think your amp is probably at the limit. Those speakers are rated for up to 500 Watts, but have a very high sensitivity (96 dB).

Your amp is 150 Watts/CH which might be a little small. 250 Watts or more might get you were you want to go.

However nice those drivers are, they do have output limits. You will eventually reach driver compression limits.

Changes in character of sound at high playback could also be acoustic interference with the amp. Have you experimented with isolation footers of any sort. As I’ve upgraded the footers under my power amps their ability to play back at high levels without any issues was completely transformed. 

What other similarly priced alternatives have you auditioned the Personas against?  Logic suggests that at the price level you're operating at, there will be other makes out there that do it all for you, with no need to make allowances for certain listening conditions.