When you say "any input will be appreciated", you're asking for trouble!
I don't think replacing the receiver is going to give you any "wow" at all.
How much HT/Music? If you're spending a lot of time "listening" to the center channel, you'd probably see a pretty big improvement by upgrading it. Same deal with the surrounds; if they are direct-radiating and not of the quality you'd like, you'll probably see a dramatic improvement in HT experience by moving up to the QS4 or QS8's.
If I were in your position, I'd probably upgrade the surrounds, the center, the sub, and the receiver in that order, keeping the M22's as mains.
