Haven't checked the entire thread, and I'm sure someone mentioned this, but have you checked the polarity of each driver to make sure they are pumping in unison.
I like the mids from my M80s even though I have only used solid state amplification with them (Yamaha M80 monsters, first 30 watts in pure class A). I picked up an Integra Research RDA7 but haven't set up the system since my flood.
I prefer tube amplification (and tube preamplication), but have to say the M80s sound excellent even driven by sand amps.
Good luck to you!
