I run an Onkyo 797 and have used it with 4 ohm speakers (KEFs) before. The M80s present a rather light 4 ohm load compared to some, but i cannot vouch for the capabilities of that particular receiver with a 4 ohm load.
It should be find for most reasonable sound levels. Worst case scenario, you could always take the receiver back (assuming you do not already own it).

"Those who preach the myths of audio are ignorant of truth."