I'm looking for a receiver for my main music setup (secondary TV setup). Right now it's wired for 5.1 and I really can't go beyond that because of room layout. So I think I'm ready to pick up a HK 520-z or 525-z refurb. All the while I'm thinking - what a waste, I'll never use 7.1, then I come across an HK 510-z at the Harmon Audio site for $100 cheaper than the 520. It looks like the main difference is that it's a 5.1 receiver. Anyone know of any other significant differences that should sway me to buy the 520 instead?