Unfortunately the application of the concept of slew rate is poorly understood in audio. It is good to explain why something sounds poor because it is inadequate, but little else. What is meant by
"the theory that extraordinary capability implies ordinary demands are effortlessly met" ?
I agree that Atmasphere have pretty good micro-dynamic expression. But I have owned several generations of Atmasphere equipment, starting with a first generation MP1 and a M50, all having similar claims of high slew rate and having very different micro-dynamic expression - the Mk3.2 was a big jump over previous ones. IMHO we must look elsewhere for an explanation of their great micro-dynamic expression, perhaps to the particular spectral behavior of the distortion of the Atmasphere amplifiers. Surely, I am just divagating, no proof of any kind of it!
We must remember he can have now ultra fast operational amplifiers with slew rate of 6000V/microsecond! Will they sound great?
Concerning your observation of speaker matching, this can be a serious issue unless we are addressing the M2's. When we look around very few top high-end speakers are fully compatible with those OTLs, narrowing its use to a few speakers.