Acoustic Zen Crescendo

An OTL would surely welcome a nice easy to drive 12 ohm load, this makes perfect sense. The Triode Corp and Line Magnetic SET amps do very well with the Cresendo's  6 ohm flat load. Both of these have terrific quality output transformers and serious stout power supplies.This is why these amplifiers are so heavy (and sound so divine).
Charles

Wig,

It looks like your amplifier progression was VAC 160i, Vitus RI 100, LM 508ia. Not a dog in that group.
Charles

Lots of amp/pre-amps within the last 7 years:

Belles 350A/Belles 21A Modded caps/power supplies
Herron M1 Mono Amps/ Herron VTSP-3A Pre (loved it)
Vac 160i
Vitus
LM

Speaker:
Vandersteen 2CE Sig II
Avalon Ascendant
AZ

Wig

Thanks for the comments guys. Sksos, I used the Zeros for the same exact reason which suggests to me you wanted better bass, volume, and dynamics with the M60 rated at 60 watts. That is my current issue with tube amps rated at 60 watts with the Crescendos. I am missing last last bit of refinement and control at higher volumes. This is not to say the sound is not beautiful, as it is, however better control at higher volumes is a nice to have also.

Wig, one final question. How large is your room and at what volume do you listen when off the leash? Thanks again. Remember, my room is very large as mentioned above. When off the leach I measure sound levels at 90 - 92 db weighted slow C range. 

Charles being happy or not is a purely individual subjective determination. Its fine as a personal recommendation to like minded individuals but not reliable to predict what will happen with the next random guy who tries. How many people are "happy" with a particular solution is a much better indicator.

Just saying...