My understanding is that the difference is mostly in two areas -- a bit more deep bass, and the ability to play louder than the M60 and still sound good. The M80 is the M60 for big rooms.

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