Zach - As I said before, I've never heard the Axioms but they come highly recommended by many. Others can correct me if I'm wrong, but from my reading, my sense of things is that the Axioms would be more comparable to Paradigm's Studio series; they are supposed to be that good.
That said, if you can get that kind of discount on the Polk RTi's, you'd be foolish not to at least give them a serious listen. That's one helluva discount; the kind that can't be ignored. If, after listening to them, they don't tickle your fancy, I'd make an effort to audition the Axioms (see RJB's post).
Everything's relative but the kind of money you're talking about is a lot of money to most people. Before you spend it, you owe it to yourself to audition all three systems (four if you count Aperion). At least try to audition the main speakers of each system. Then you can make a decision that will result in your being very satisfied with your purchase.