just a different thought; even though you love the way it sounds, you'd probably be better off spending the tax money on matching mains to your new Polk center for a seamless front soundstage. Surrounds don't particularly need to match, nor do they need to be terribly spendy. Depending on the size of your room (which is?), a good budget for a good sub is key.
I know this doesn't address your question, but food for thought nonetheless.
Nothing like doom metal in the morning to get you going