No, I don't think they're a 2 ohm load; if they're on different amps, they're on different amps, and they're a 4 ohm load each.
I think the real question here is, "Why do you need 2 M80s per channel?!"
WHY NOT! lolololololololololololololol
Actually, the layout of my house is open. So much so that the opposing wall from the M80s is 60ft away. There is furniture, a partial wall and a pool table between but that is it. Sounds great under the pool table but I can't really get into the groove from there!
So the second set is there to help fill the room with sound. I was also considering adding another system on the opposing wall and wiring them together to work in unison. That way BEER CAN CRUSHING POWER can be had from anywhere in the room!
My only worry was being able to sync the sound from 2 different amps (even if the same make and model) when they are 60ft apart.