Thanks for all the input guys, consensus seems it's not justifiable to add an external processor and amp except when you need more headroom, which in reality I don't. What I want really is just a few new aspects of technology (auto cal/Eq, HDMI 1.3 receiver). I always felt this invisible pressure (probably by reviews/magazines as part of the never ending marketing ploy) that my speakers are "missing" their potential without greater, cleaner power. But Axioms are sensitive, pretty easy to drive, so It's hogwash I guess.
Micah, out of curiosity, you use the XPA-3. So how does that work for your backs? The Denon is the preamp for all 5, but only sends power to the 2 QS8s? I've never come across that approach before.
