I have M60 ti's and v4's (ti's in the HT system, v4's in the music system).

For music I find the v4s a noticeable improvement. For HT I wouldn't bother... it seems that relatively more movie audio is well balanced/mixed than music recordings these days, but whatever it is I like the sound of the ti's just fine the way they are.

Not sure how applicable my experience is to your M80 decision though.

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