SET amps with cajones and finesse

Avguy does make the most important point. A speaker's rated efficiency is only 1/3 of the question. That speaker has to have a very benign impedance curve and phase angle through the crossover in order to properly use an SET of under, say, 35-40wts. A speaker with 90db eff. but a difficult imp. curve and phase angle will not respond to a 5-20 wt amp. I have ProAc 2.5s which are 87db but have an extremely easy imp. curve and phase angle - I easily drive them with a 9 wt AirTight 300B amp. I am in a small, plaster room, though.

Despite the high sensitivity of the Klipsch horns, the large woofers REQUIRE high power.

While I have a pair of AtmaSphere OTL amps, I will say I have tried the Zero autoformers in my system, and they really bleached out the sound, and robbed the Atmas of what they do so well. The end result was clear and fast and sterile, and, well... it was if they became a solid state amp.

I will agree that an 845 based tube amp will also be a great suggestion. The ASL 1009 I have heard combined incredible slam and lovely sonics.

Cary 805's, of course. They provide SET magic and a bigness to the sound, to boot.