Hi bwallen,
I'd be reluctant to try and drive the three 4-ohm M80s with an inexpensive Yamaha. I'd hedge my bets and get a Denon, because I know the entry-level Denons have no problems--and have never had trouble--driving 4-ohm loads.
Whichever brand you decide to get, if there is an impedance setting, always leave the impedance switch at the highest setting for the 4-ohm M80s. Using a lower impedance switch setting on the receiver will reduce the receiver's power output significantly into 4 ohms; it inserts a voltage limiter into the circuit, thus reducing power output.
With reduced power output, you could drive the three M80s into clipping, resulting in potential damage to the drivers.
Regards,
Alan
