In a 7.1 setup the two rear speakers are mono, so both left and right rear outputs are delivering the same signal to the speakers. Either one should provide an acceptible signal for 6.1.
_________________________
HT:
990/770
Oppo BD83SE
Pioneer Elite DV-47A
Magnavox HDMR513h DVR/DVD-R
Sony DVD megachangers-2
Sony CD megachangers-2
Monster power centers-2
Sony 48" rear projection SDTV
Roku video player
JVC AL-A158 Turntable
Polk RT-2000s,CS-650,XS-650s,RT80s
LFM-1EX
Hsu VTF-1
12" Velodyne

Family room:
OPPO 970
Sony 32" direct view HDTV
Denon 3801
Rolk RMs