Hi Ken,
Historically, I used to advise forum members who were getting the 4-ohm M80s to avoid Yamaha and Onkyo and go with Denon, whose receivers generally seemed to be more stable into 4-ohm loads---even the entry-level models.
Since then, Yamaha and ONkyo have some upper-tier expensive units that will support 4-ohm loads. However, I think it's a bit "iffy" for you on the model you're considering if you use the VP-180 with M80 mains, ESPECIALLY in the huge room. Receivers just do not have huge power supplies and endless amounts of power into low impedances. If you want really excessively loud (to me) playback in huge rooms (and the M80s will do it cleanly when fed hundreds of clean watts), then you'll need an outboard power amp. If you use the VP150, it's easy to drive and a decent center (no match for the VP180) until such time as you have the stable 4-ohm power for all three front channels. You might find a Denon AV receiver that will do that right now if you don't demand ear-deafening playback like some demand.
Cheers,
Alan
B
