Ok, I see Peter. I had a similar situation in my previous home so I understand.
I'm looking at the M60's now for my wifes room which is approx the same size as my theater room (19x13x8) except my theater room has vaulted ceilings @ 10 feet, and she had her eye on the smaller M60's, but I thought we might be able to swing the M80's in that size of a room. Maybe not though.
Anyway, I was just curious since the consensus is you should be 10'+ from the M60's and 13'+ for the M80's. Seems like alot of "breathing room".
