Scott, I agree that a third M80 used as the center is the ideal solution when it can be placed properly, as it can be in your setup.
The 125 watt 7008 should have ample power for your needs, unless you listen at an extremely loud(and dangerous to hearing)level or at an unusually long distance. There should be no good reason to spend money on an additional separate amplifier.
Because of the relatively close proximity of the back surrounds in your setup, the wider dispersion of the QSs would be the preferred choice.
