On my HK 7200 I have the option of using the second set of rear speaker inputs as part of the 7.1 system or to power a set of speakers in a separate room. Just have to make a change in the menu.
I'm running a 5.1 set-up. The receiver doesn't sense any speaker connections for the extra rears and sends no signal. There is a graphic on the front of the receiver which shows which channels are running. The speaker icons blink when switching between sound formats (DD5.1 to DTS) because there is no signal for a second.
Unless I move to a larger room, those second inputs will not be used. But I like having that option.
