A few months ago I answered this question more or less in an another thread.
I was still within my return period after buying an HK AVR525 (which I supremely love), and figured I'd share my research obsession with another poster who was considering, at the time, the choice that you now have before you.
Do a search for my name "h1pst3r" or "AVR525" or HK...you get it. Take a read through and then fire off any questions you have.
I can tell you, I absolutely love the 525...!