If you're running 5.1 in main room, you can use the extra rear channels to power the 2nd zone. Reassign the amps (pg. 10). Set the zone volume control option (pg. 15). Turn multi-zone/source use on (pgs. 25/26). One thing to note is that the 2nd zone uses analog signals only so each source you want to use must be also connected using the analog stereo connections. If running 7.1, you'll need a separate stereo amp.
