In most 7.1 systems, the surround back channels are mono (same signal to channels 6 and 7), in which case those of us (myself included) with only a 6.1 speaker setup can get by fine. I don't know yet how the 7.1 stereo mode works on the 950 to know if the left and right surround back channels get discrete signals, or if there is a way to tell the 950 that there is only one surround back channel. I suspect that you'll be fine, but we won't know for sure until we can get our hands on a manual.
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Gonk