Ken, wasn't your comparison flawed, shorting bars on the back of the M80s loose or something like that?
In my experience, the M3's are different tonaly than the M22 and M80s. The M80s and M22s have a much cleaner midrange to them. That dip in FR makes voices from the M3s sound to be behind the other sounds rather than in front of or equal to. Now this was all with v2's and my Ti M22's so with v3's, YMMV.
With certain male voices the M3's like to add a fat or bloated characteristic to them. The wonderful jazz vocalist Kurt Elling comes to mind. Female speech/vocals sound better IMO. I think this comes from the mid-bass hump and voicing on the M3 which has this effect on the speech region.
Based on the on-axis response curves, the M2 and M22 does not have that characteristic. Like Grunt and JohnK also mentioned they would be a better tonal match for the M60 than the M3 and would also give you more natural vocals/speech out of the centre.
The only concerns I would have with the M2 is power handling and being able to keep up with the M60's during dynamic movie passages and speech intelligibility in large rooms at further listening distances. How large of a room is your theatre, listening distance etc?
