I have to respectfully disagree with the previous posters on some points, but agree on one.
First off, I don't believe that a system of M80s and a 500 will "overpower" your room. Although I own M60s and not M80s, I've found that Axiom speakers can sound extremely good with lower power levels and in a small room (mine is 13' square).
I do, however, think that your question is a valid one. My previous (non-Axiom) floorstanding speakers just sounded completely lifeless without cranking them up. Likewise, I have a system in my studio that combines some old Design Acoustics PointSource bookshelf speakers with some Cambridge Soundworks passive subs (an unusual scenario, I'll grant you) and have the same exact problem. At lower levels, it's just completely lifeless. When cranked up a bit, the setup doesn't sound bad.
I don't have an explanation for this. I'm not a believer in esoteric cables or little tripods to hold the cables off the floor, wooden knobs, power cables that improve the sound, etc..etc..etc… I understand that "louder sounds better" in a general sense. I wouldn't A/B speakers unless they were matched extremely well for volume.
Yet, rational explanation or not, to me, some speakers just don't sound good until they have some decent power applied to them. Some day when I have time to kill (HA!), I'll pull out an SPL meter and graph the system at two or three volume levels to see if there's some non-linearity thing happening.
I think most can agree that if you placed a gigantic, stadium-sized PA system in a bedroom, it's not likely that the setup would sound good as it's inappropriately-sized for the application. That's an extreme example, but I think it illustrates that there ARE times when you can have too much speaker for a room.
In this case, though, I don't think you have anything to worry about. Axioms don't seem to have that problem and I think they'll do very well for you!
