Assume you're auditioning in a store? Why spend so much on the AVR compared to the speakers? I'd spend more on speakers less on the avr as it seems your total budget could handle that. For the center why not a third 685, that would be the best way to match or are you looking for the traditional sideways configuration of the center? I listened to a pair of 685s and wasn't all that impressed personally, ended up with Ascends (ID brand). What subs are you considering? I'd definitely go ID for the sub.