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

I agree with the above post. Try a different tube preamp. That can make a large difference. Going to the Bryston is a waste of time imo.

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.