This seems more like an amp question. Any un-used channels on the 976 cannot be re-assigned to the L/R channels for instance. The 976 can output a channel signal which would then have to be split between two amp channels and fed to the bi-amp connections on your speakers. Since you would be bypassing the internal crossover of the speaker it would need some sort of external active crossover if for nothing else to prevent destroying the tweeters.
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Music system
Model 990/7500/Magnepan 1.6 QRs/Technics SL1200 MK2/Aperion S-12 Subwoofer/OWA3/Sony NS75H DVD
APC H15 Power Conditioner

TV System
Large Advent Loudspeakers/ Polk center/Monoprice surrounds/Panasonic Viera 42 inch/Onkyo HT-RC260/Sony BDP S590/Directv


Home Theater System
Onkyo PR-SC886/Outlaw 7125 Klipsch RF-82 L/R,RC-62 center, RB-35 SR/SL, BENQ HT1075, Outlaw LFM1-EX/OPPO BDP-83/Directv
Harmony ONE
Blue Jeans and Monoprice interconnects
APC H15 Power Conditioner