I currently have a HK520 that I'm using as pre/pro. I like the fact that I can reassign the internal amps which I have done to power my Rockustics. I can re-assign 2 more amps if I decide to go to 7.1. I paid $399 from CC (open box) and the unit has worked flawlessly except for a problem with the volume control knob. When turning the knob rapidly to lower the volume, the volume occasionally goes up or stays the same. HK was notified and will fix the problem at no cost. I'm also still within the 30 day return period. Onecall has the HK525 B-stock for $499. Besides the 2 extra amps, DD EX and triple crossover, would I gain a significant improvement in sound if I swapped out recievers? I would lose the ability to re-assign amps with the 525 but I think I can re-assign the rear surrounds to power the patio speakers, but then I would lose the ability to to go 7.1 in the future unless I get another external amp. For $100, is it worth it? Is DD EX that important? Does the 525 offer superior sound to the 520? If yes, is it drastically superior?