If I bought this 7 channel amp and was using
only 5 channels, would each of the 5 channels
get some of the power from the two used
channels? If yes, how much more power would the 5 channels get?

I am not sure. I have a 770 but am only using 5 channels at this time.
DmC

If I read the manual properly, each amplifier channel is discrete (separate power, separate circuitry) so there should _NOT_ be any power re-distribution if you are not using channels. This is done on purpose to avoid "cross-talk" (bleeding of sound from one channel into another). I am not an authority on the subject, but that's how I read the specs.

There are two transformers that are shared across all seven channels. I don't know which four share the one and which three share the other.

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Matthew J. Hill
matt@idsi.net