set vs otl, which is the most musical

Boa2, in response to your question, amps designed for Class A operation all run hot, whether OTL or not, whether tube or solid state. It's the Class A operation, not the fact that they are OTLs, that results in the heat. The best of the OTL amps (Atma-Sphere, Joule, Tenor) are run in Class A for best sound. For a while, Atma-Sphere made the MA-1 and MA-2 models with an optional switch to change operation from Class A to Class A/B to address the heat issue, but I think Ralph dropped that as a standard feature because most owners never wanted to make the sonic trade-off and left the amps set for Class A anyway.

[D]o the OTL's and their little tube armies run especially hot?

I am not a techie, but I think that Howard has put his finger on one of the heat issues. I could be wrong, since I have no personal understanding of circuit design, but I think that large number of output tubes needed for an OTL design, along with the Class A operation, contributes to the heat load. And then all of those driver and input tubes. My Atma M60s each have 12 tubes (so thats 24 for stereo) and my Joule VZN-80 has 16 tubes total (including 8 of those Russian monsters). Put it all together and the heat is an issue, but one I have chosen to live with.

Thanks everyone for the info. We've previously had amps that heated the entire upstairs of our apartment, as well as running up the electricity bill. I think if we had more space, and a quieter AC system, I'd jump at the chance to hear the OTL's. The only one I've heard represents merely a toe dip into the pool of OTL's. Jax2 came through last year with his Berning MicroZOTL, and we ran it through our Klipschorns. Understandably, it's 1 watt didn't lend much weight to the music, but oh my did the vocals sound delicious.

The Moscode 401HR is OTL. Runs reasonably cool...

My Trios sounded not so good with an Atma-sphere M60. I think there is some impedence dips in the highs. The highs were rolled off. My Viva Auroras 845 are a perfect match. With my Silverline Sinfonias the M60 were very good. They are a flat 8 ohms. I still liked the Vivas better though. Way more goose bumps. I didn't find in my comparisons The M60 gives much of that. This is just my findings with my equipment. Others I'm sure might find different. OTLs do definatley need flat impedance. 8ohms or higher.
Steve.