I could have sworn that I read something to that effect right here on the Axiom site. Maybe one of Alan's posts.
From the review, "The M80ti was fussier to set up than the M60ti, and needed a lot of adjustment of positions to sound its best with bass-heavy music.".
In my acoustically challenged room (16x16x9, 1 loveseat, no wall hangings, bare hardwood floor, curtains on 2 walls), I can make the exact same claim about the M60s. Every time I move something into or out of the room, I have to adjust my speakers. I'm remodeling, so things are shifting from room to room all the time. Needless to say, the room is very boomy and has lots of echos. I can always find a place to put the speakers so that they sound fantastic again, it just takes moving them a few inches one way or another to get them there.
I'll bet that it is simply the fact that the M80s have more sources of sound waves (even at the same SPL) than the M60s do. The listening environment must now deal with the reflections of sound waves from 12 different "point sources" of sound instead of the 8 that it does with the M60s.
I doubt that it has anything to do with the engineering of the speakers. The reviewer's listening environment might just be more conducive to dealing with the M60s than the M80s.
The reviewer only stated that they were fussy, not impossible. Hehe... maybe he bought female M60s?
ducking... 
