Thanks for your feedback guys, appreciate your thoughts. You've pretty much confirmed my own thoughts and made my decision a lot easier.

JohnK, when I get my new speakers, I'll definitely experiment with the M3's firing at the back wall. Hadn't thought of that before to be honest.

I'm going to buy a pair of M22's and use the M3's as surrounds for now. Mate them up with an svs sub and the Whatmough P2 centre channel I have and I should have a pretty awesome set-up!