The M3's will match best with the M40, or M50 towers. Or you could just use another pair of M3's as mains.

What I would do though, is use the M2i as rear surrounds and get a pair of M22's as mains (or M60's if you want to go all out).

The M3, M40 and M50 are Axiom's more "laid" back speakers. The M2, M22, M60 and M80's are Axiom's better known, crisp, clear, more "forward" sounding speakers. It would be best if your fronts and mains were from the same sounding "family".

Good Luck - and have fun!