This is a shot in the dark, and I recognize that Thiel's balance is tilted towards the treble in most of their earlier models, but I will note that long ago when I owned Duntech Princesses, not a particularly bright speaker by any means, I was troubled for a while with a very slight upper midrange/treble glare similar to what you're describing. It turned out that the culprit was the Purist Colossus, original version, speaker cable that I was using, which had just a small touch of extra presence/energy in that area but was otherwise a great-sounding cable in my system. This particular characteristic is not present in other, later (and pricier) Purist cables I've heard, nor with the Dunlavy speaker cable with which I replaced the Purist. If there's a way for you to borrow another set of Purist cables, say Proteus or one of their newer lines, it might be worthwhile to see if and how much the cable is contributing to the problem you're experiencing before you do your speaker upgrade.
Piego P-10 or big Thiels?
Considering upgrade from Thiel 2 2 to bigger Thiels (6 or 7.2) or perhaps a different route to the Piego P-10.
Any advice on speaker selection?
I like the Thiel sound a lot, but find this system to be a bit bright on sibilants like Holly Cole Trio "I Can See Clearly Now...", and less detailed than other kilobuck speakers. Sometimes - esp. on upper piano - brightness approaches a glare. Wife and I are not satisfied with B&W sound or MLogan/Maggie space requirements.
Gear is:
AudioAlchemy DDS-Pro
Wireworld Gold Eclipse balanced
AA DTI-Pro
silver I2S
AA DDEv3
PAD Colossus I/C
BAT VK-3i,
ProSilway II balanced I/C
BAT VK-500,
PAD Colossus speaker wire
Thiel 2 2
and preamp to Velodyne F-1500R
I'll eventually upgrade digital gear to Wadia 861 and run it straight into the amp.
Room is medium size with vaulted high ceiling and open to other rooms.
Music preference is no country, limited opera. All CD.