It does have pre outs, but do you really think that timing would be an issue for the rear surround channels? Since the front left, right, center and sub would all be fed directly by the oppo the rear left and rear right would be the only channels sent to the receiver ... I just thought the more direct/pure the connection is the better ...?
You still have to worry about levels. You'd be controlling the amped channels with the player and the rest with the AVR. Connecting amps to the AVRs pre-out eliminates that issue.