I've played with the bass levels on the M22s but it has had limited effect when trying to achieve "full" sound.
Then the M3 option isn't going to add much as they do not play any lower than the M22s, I think you are now at an impasse and have to decide if you want true full sound either with subs or finding room for M80s.
I will take a guess and say it is the midbass or rather the lack of it that you are noticing and that is the one thing I noticed was lacking with M22/sub combo. The combo is very close to sounding like a full range floor stander but the mid bass just doesn't get the same attention.
I can definitely envisioning that exact problem walking around the room. At the same time, all the speakers are mount in corners and the seating is centered in the main room, so for sitting and listening it would probably work.
I would say not so fast, you would hear that tonal difference coming from the back and front at all times just not when moving around, it would just be even more noticeable when moving about the room.
