i would definitely get some M60's for the space. 80's not needed. and you just cant go wrong with SVS, but take a look at the new axiom subs. EP500 and EP600. they are rather expensive, but all indications go to show that those subs are setting new industry standards.
i would also suggest the VP150 center, and some QS8's. the VP100 and QS4's could get the job done, but why leave yourself in a position to wonder 'what if'?
it sounds as though you have a pretty killer HT set up already. i would love to see some pics of your dedicated room, and its a must once you get your new axioms.
bigjohn