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

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.

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.  

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.

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.