I could not be happier (perhaps ignorance is bliss) with my M-60s. I'd be at a loss to imagine how they could be improved upon with respect to sound. Not saying the M-60s are the worlds best sounding amps, just saying that my 3.3s with the current tube complement have not been bettered by anything I personally have heard at any price.This is all about the way the loudspeaker and amplifier work together. Some speakers don't like a lot of damping and then our OTLs play them nicely. Other loudspeakers simply can't be driven well by any tube amp without feedback; that's what the class D is for. In both cases the idea is to minimize higher ordered harmonic production and IMD to prevent harshness.
Someday maybe there will be a 'universal amplifier' but IMO that's still a ways off.
Thanks for all your comments :) Have a Happy Thanksgiving!