I assume you'd just hook up your center rear speaker to the left rear input on the 978, the way I do with my Integra DHC-80.2. I think most high end AVRs and pre-pros with 7-channel surround use just the left rear channel to accommodate a 6.1 system.
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HT:
Outlaw 7700 amp
Integra DHC-80.3 pre-pro
Oppo BDP-105
AppleTV
TiVo XL Premiere
XBox 360

Legacy Whisper XD fronts
Legacy Focus center, sub, surround and surround back
Shunyata Defender conditioner

2-Channel:
Parasound Halo JC-1 monoblocks
McIntosh C2500 preamp
E.A.R. 324 phono stage
AMG Viella V12 turntable
Lyra Etna cartridge
VPI SDS

Kubala-Sosna Elation interconnects
Kubala-Sosna Elation speaker cable
Shunyata Triton & Typhon power conditioner


A man's reach should always exceed his grasp ... else, what's there a Heaven for?