Troy, it's unlikely that you'd have a significant audible difference between the M60 and M80 with the SVS sub handling the bass below 80Hz. Both use the same two 6 1/2" woofers, and the larger M80 enclosure allows for tuning it a few Hz lower, but this wouldn't be meaningful with the sub handling that area anyway. The other difference is that the M80 uses dual mid-range drivers and tweeters and this would allow for a higher and cleaner maximum output level, but unless you were listening at an extremely loud level this also wouldn't be meaningful to you.
I don't recall Alan making a comment supporting putting a small sub on each surround. If you mean that you'd connect the receiver surround pre-outs to those subs, then it would be almost meaningless, since there would be an 80Hz or whatever crossover which would prevent the "surround sub" from doing much. In any case, the surround bass being handled by your main sub should be entirely satisfactory.
I'll also add that using only a 2.1 setup for a mainly music system is an unnecessary limitation on your enjoyment of that music. Using a mode such as DPLII to extract the surround ambience mixed into two channel material(there was no place else to put it)and direct it to the surrounds where it belongs, is a very significant improvement in realism.
