Hey Tom, its a logical extension of this discussion of tube and SS amps. Like alot of stuff in audio you are going to get supporters and detractors about it. The idea has some merit since tubes on top and SS on the bottem supposedly plays to the relative strength of each topology. I can only share my own experience in that regard and YMMV. I didn't try bi-amping tubes and SS on an M80 but I suspect the issues involved would be much the same.
Firstly I used a 1400-2 to drive some 10" woofers and a McIntosh MC2102 to drive the other drivers. That sounded crappy for several reasons: the gain of the 2 amps was quite different so it threw off the speakers amplitude response, and the phase of the amps wasn't the same so I sensed timing was off or a lack of coherency as they say. Moreover both amps were still powering the speaker through its internal crossover network which had been optimized for a single amp and was likely causing further anomolies.
So I picked up an external crossover, first a DBX 223XL and then a Bryston 10B. I could adjust the crossover point and slope, gain, and with the 10B, phase. I spent several months tweaking to get the amps to mesh smoothly and while the 10B in particular really helped the speaker never really sounded coherent. I didn't feel like opening up and taking out the speakers internal crossover which some folks suggested so I abandoned that experiment instead after several months. So when people talk of biamping now I gently suggest using one amp or identical amps.
I'm sure alot depends on the speaker, amps and the room acoustics but there is too much hit and miss involved. Even if you get the gain right, its almost impossible to align phase across the band where the two amps overlap because of their different characteristics. After all what's being attempted in a way messes up the crossover network which was carefully designed for the particular speaker.
Recently a friend of mine has been trying to bi-amp a Martin Logan Summit (electrostat and cone drivers are already tough to time align ) with tubes and SS and to my ears it does not sound nearly as good as with one amp either, but he likes the sound and that's what counts. Besides much of the fun in audio comes from trying to get the best sound from our gear.
