Hi,
That's a huge room you have (over 5,000 cu. ft.) so you may find that any AV receiver may have overheating/shut-down problems when driven to very loud playback levels in such a large room. But it's very dependent on your own preferences in playback volume, and listening distance.
That said, the brands of AV receivers that Axiom has historically found have no trouble with 4-ohm M80s are Denon, Sherwood Newcastle, NAD, Outlaw Audio and B&K.
You could always consider adding a couple of outboard mono power amps for the left and right front channels (M80s) and use your Onkyo for the other channels.
Regards,
Alan
