I used to have an M22 plus STF-2; it is a great combination. I'm sure Axiom's subs are good also; just mentioning I had the combo you mentioned. You'll be very satisfied with it.

I haven't heard the Studio 20, but auditioned the Monitor 3, although not back-to-back with M22s. I liked the Monitor 3 a lot -- good sound and bass for that size speaker. However my impression is the M22s have better detail, and with a sub vastly more bass.