Unless you -really- need more bass out of your surrounds, I can't see much improvement being made. Seeing as you have 2 subs in your system already, I'm guessing most of the LFE is directed there anyways.

Not knowing what model of sunfire subs you have, that's probably where I would look first. Next up would be beefing up the M22's as your seem to have plenty of power to drive much bigger fronts. Your center is already top notch but that would be the next place I'd look after subs and fronts.