What subs are you running ATM. At one point during my HT addiction i was running a Denon AVR 3311 which is a fairly decent receiver (still in service ) and i added a Emotiva 3 channel amp and the difference was huge. I dont play movies loud and it was not that kind of change, it was fullness and cohesion of the sound that i experienced. Now people say amps dont sound different, i happen to think they do, and some say its expectation bias i say BS. I added the amp and my boys noticed the difference and they did not know the amp had been added. If you dont want to take the chance find someone to borrow one from or buy one with a 30 day return, i highly doubt you will return it.
I think with the M22's you should run you sub a bit higher , i recommend crossing over at 120hz unless your sub is a long ways away from the mains. I had M2's for a short period and they sounded great but i had to play the sub up a little to compensate.