With those latest models by Onkyo, you most likely will have no problems driving the m80's. I've always owned Denon, so maybe some of the Onkyo owners will chime in...
I own an Onkyo 797 and never had any problems running 4 ohms speakers in the past, the last pair being tested were Kefs.
However, i bought a used Anthem amp, MCA30, for $650. You can get the MCA2 or MCA20s for even less, again on the used market.
"Those who preach the myths of audio are ignorant of truth."