You would use a standard phono lead to connect the 3803 to a power amp.
Power amps are just the amp, they do not have a pre-amp ie volume control or input selection etc. Everything on a power amp would be controlled by the 3803. If you got an integrated amp with volume control etc then it is likely that you would need to set the volume on both of them. However some integrateds like my Arcam Alpha 8r have a processor mode that bypasses the preamp when being fed from my 3802. This is available on other makes of amps, but not all makes or even models have it.
The advantage of the integrated over the power is that for stereo music I plug my CD player etc into the Arcam and bypass the 3802. The preamp in the Arcam is far better for music than any AV receiver in this price range. If music replay is not a priority for you then just go for a power amp.
Mark.