15 words or less: with the 770, you really don't.

With an amp like the 770, the only reason that you really care is that the power output at 4 ohm is a bit greater (which might make a difference if you had really low efficiency 4 ohm speakers and needed the 300 watts produced by the 770 with a 4 ohm load). With many receivers, however, the built-in amplification may not be able to support a 4 ohm or lower load. Dedicated power amps generally are more robust designs that can handle it.

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