classe ca-300 or bryston 4b sst for thiel 2.4

I agree with with the observations of fellow A'goners. Keep the Classe amp and try another pre. It seems that you would be making a 'lateral' move with the Bryston. I might recommend a BAT pre., nice and warm and no harshness or brightness. Just my 2 cents...

i had a 4bsst that i sold to lower my investment in gear due to other priorities. replaced with B&K monoblocks - the 4bsst was definitely warmer and low end extenstion for day. driving a pair of Boston Lynnfield 500L's this is the best amp i had used to date. (ive had proceed, aragon, adcom, ayre and legacy...) the ayre would be the choice if it had more power - imo.
plenty of power to satisfy these inefficient speakers. i have never audiotioned a Classe in my system although i have heard good things about them. if you can save $1000 or so on the bryston i would think that is the way to go. not the absolute last word in resolution however. i heard esl makes an amp that has huge current and great sonics - maybe worth a try?

Well I might help you as it seems we have the same problem. I currently have 2.3 with MAC C2200 tube pre to MA252 SS power amp. I think overall sound is a little to vailed and bass does not kick the way it should. I demoed 4Bsst and found bass to be great. What I also liked was low SPL bass presence I do not get with MAC power amp. I certainly wouldn't call Bryston in my set-up bright. Highs are more present compared to MAC (and I like that). Mids are not so great as thru MAC though. Sound is with no question leaner and dryier thru Bryston. But still I think I would do better getting Bryston.
Mac sounds very good when played very loud. Most of the time I listen low SPL and then I like bryston more.
Cables are Transparent Super, CDP Jolida 100A

I love my SST stuff, but I agree with others here; try a different preamp. I would also recommend that you try some Analysis Plus interconnect and Oval 9 speaker cables. They are a fuller-sounding but very (subjectively) quiet cable combo with powerful bass and smooth highs.

Lets see, Classe cd players are a bit on the cool or edgy side...coupled with a preamp that is on the light side, and adding in the Thiels which are also known to be a bit "bright". Ouch. It does sound like negative synergy here. I don't know what Accustic Zen sounds like so....I would say that your amp is not your problem. Also, you might want to consider a tubed cd-player. In fact, they might be the first place to try.

Your room, with hardwood floors and no rugs, may be contributing to your brightness problem. The 2.4 has excellent bass but it is tight and not bloated or overly warm; you may feel it is too lean. If you have not aggressively broken in the speakers, you might want start there--play them loudly for a good 100 hours or more with a variety of dynamic music. It can improve the bass.

I own 2.4's by the way.