SET 45 Amp Driving Dynamic Speakers

Hello Inna,
I can’t honestly say that I know your musical/listening taste, rather I recognize that you prefer amplifiers of a certain power range. My taste is unambiguously towards the natural/organic sound with tactile realism.
The Concert Fidelity  SS amplifiers do that exceptionally well. I’ve only heard them with their sibling tube Line Stage which only further helps I’m sure. It’s a pure and natural sound character rather than electronic (the bane of many SS amplifiers IMO).
Charles,

I am using a Yamamoto A08S SET 45 with EML mesh tubes, driving a pair of Zu Audio Druids in a dedicated listening room about 15'x18' and the result is just stunning.
The transparency, detail, tempo, balance and realism is far beyond anything I've ever owned before, or even heard with other people's systems, some costing 10x and more. The cost of my amp + speakers (new) is less than $9K. I couldn't be happier with this setup.
True, it doesn't play nearly as loud as my living room 60lbs, 700 Watt Classe SS amplifier, and I don't expect it to.
When I want to turn the volume up and listen to hard rock, metal or electronic music at live concert levels, I do it in my living room with a system that excels at that :-)
Maybe one can have both worlds. I haven't found that setup yet, but I can only guess is that if it does exist, it will probably cost 20x more than both my systems together.

Ami, that's one of the things that I said - two very different systems.
Charles, of course I like what you do as well. But that's not all. Even flamenco music requires speed an drive let alone Mahavishnu Orchestra's jazz fusion. Bass is important too. Not exaggerated, but just as it was recorded.
It does appear that I strongly gravitate to Lamm/Atma-Sphere camp. Never heard VAC or Allnic let alone Ypsilon and Absolare.

I'd read a lot about 45-based amps requiring very efficient speakers (over 100dB), but I've run 45 amps by Korneff, Burgess and Yamamoto with Vaughn Triode speakers (97dB) with great success. 

My room is 21'x19', I generally don't listen to very loud music (in the mid-70dB range) , but the system was capable of much more and with a wide variety of music. 

Ultimately, I went back to Harbeth with a high-powered SS amp, but I do miss the lushness and intimacy of the 45. 

Hello Ralph (Atmasphere).

I've seen your comments before and I am keeping them in mind as I design/assemble my new system, a 4-way active. If using a 45 amp to only reproduce 350 to 2000Hz on a 100 dB/W driver in a 25m2 room and if average listening level is 85-90 dB SPL, would a 45 suffice or be driven to the point where 5th order harmonics become an issue?

Thank you!