Can you get the same benefit with power amps for just the fronts and center ? Most of the content comes out from those 3 speakers AFAIK.

Dumb question maybe, but are you running the M80s in "large" or "small" mode ?

M60ti, VP180, QS8, M2ti, EP500, PC-Plus 20-39
M5HP, M40ti, Sierra-1
LFR1100 active, ADA1500-4 and -8