Rick,
You're following a similar path to what I took. I started out a few years ago with a Panasonic mini system, upgraded to a Kenwood HTIB (HTB-544) which gave me a taste of real performance but left me wanting more, and then ultimately upgraded to Axiom M22's, VP150, QS8's and SVS sub (plus a H/K AVR520 receiver).
You already have the sub part down, and I'd say you should definitely upgrade the rest if that's what you want to do. Your Onkyo speakers, like the Kenwood speakers, can sound pretty good. The designs are not that different from Axioms for example. But the overall performance of the Axioms far surpasses any HTIB speakers. Plus, good subs like SVS and HSU just scream for comparable speakers like Axiom. I'd say go for it without hesitation.
