The following observations are based on my related equipment, room conditions and personal taste. I am not a reviewer and sure as heck don’t have golden ears.
I purchased my Thiel CS 6’s new around 2000 and used these amps over the years:
B&K M200 Sonata Mono Blocks, they were anemic.
Krell 200 FPB Stereo, lots of bass punch, accurate in the midrange but the high frequencies were bright. I added a tube pre at that point and that tamed the glare slightly. Great amp for Megadeth but only so so for Mozart.
VTL 300 Deluxe Mono Blocks, they warmed up the high frequencies and added depth to the mid range but the bass was now incidental. At first I used SED Winged C 6550 power tubes and later used GL KT-88’s. I used this configuration for a few years before adding a Thiel SS1 subwoofer with the Thiel CS-6 passive crossover.
At this point I was getting tired to the maintenance requirements and tube replacement cost associated with older tube amps and started to look at going with SS amps.
Bryston 7B SST Mono Blocks, These amps (may not be the 7B, it was a long time ago) sounded nice but lacked that WOW factor. The Bryston’s were on loan from a friend who sold them soon after I returned them. He later loaned me his next amps.
Classe CAM 350 Mono Blocks. These amp were the best SS amps I’d used with the 6’s to date. They lessened the slight high frequency glare and the midrange was very close to the VTL amps and the bass was ever so slightly laid back. I returned the loaners to my friend and purchased a pair.
I kept the CAM’s for a year or so, switching between them and the VTL’s. It’s true once you've gone tubes it’s hard to go back, so later I sold the CAM’s.
Also, I tried pro audio amps: Crown and QSC. The best I can say is, not to my taste.
Note: the pre-amps used were as follows, ADCOM GTP-400, Audio Electronic Supply AE-3, ADCOM GFP-750 preamplifier, VTL 2.5 and my current Musical Fidelity A308cr. The nice thing about the ADCOM pre’s was the benign presentation, they add little or no colorization, so you really get a feel for what your up and down stream gear is performing.
These days, I use VTL 450MKII Mono Blocks which are pretty low maintenance for high powered tube amps with my B&W 801 Series 3 speakers. So, the Thiel’s collect dust for long periods of time but when in use, they still have the magic.