Before settling on an M80 / Onkyo 805 combination, I highly recommend reading this thread I started last summer. In short, I returned the 805 and went with a separate amp (Axiom 1400-8) for my M80's. I know that's a huge step up, but forum users like terzaghi have had good luck running M80's with Denon AVRs.

A: Epic 80 * 600 / Integra DTC-9.8 / A1400-8
V: Samsung HL-S6187W / Tosh HD-XA2 / PS3 / Oppo 970HD