It's the goal of the receiver to get -0 dB to be "reference", so it just may be that the M80s are that efficient.
The number on the display doesn't really mean all that much, and really can't be directly compared between receivers, and that goes doubly so for different brands.
Don't worry what the number reads, just set the volume to a comfortable listening level for you. As long as it isn't in the + range, you'll be fine (the noise floor rises quickly when you get above 0).
I've always thought the louder you had to turn it up the less efficient and more power you wasted! My Pio seems to want to turn everything down, perhaps that's a measure of efficiency but having to turn it up so much seems counter intuitive.
As I said I need to look over everything carefully before I make other changes. If I get the spl meter this weekend I'll play more. Even with my last system until I spl'ed it I wasn't completely happy!
