Disagree, unsound, with wholesale dismissal of multiple brands known to work with Thiels, including those with sub 4 ohm impedance. It’s complicated to predict the interaction between impedance and phase angle, never mind how the partnering amp will interplay. The measurements can flag models unlikely to work and those likely to work but there is a large in-between that can only be known by listening. Also, there is the room and the listener’s preference.
The Ayre AX-7 drove my CS1.6 louder than I cared for as does my AX-5 drive my CS2.4. In responding to a PM from jafant, I estimate my personal upper limit of comfort at the listening position (9’ away) to be about 85 dB. There’s about another 12 dB available before clipping with my particularly combo of amp and DAC. My experience with the CS7.2 was also powered by Ayre, either a V-1 or V-5. And my CS3.7 demo was in the Rowland room at RMAF. Wes Phillips reported that his 35 W Fisher wasn’t his first choice for the CS2.4 but “it didn’t acquit itself too badly”.
General guidance of amp brands is useful but not any more so than actual reports from users who have tried specific combos of Thiel and amp. Even for the CS5, I’m confident that there are suitable amps from most of the brands you mentioned.