The dock serial port is wired to accept exactly the same cable as one would use with just a plain player sitting on the table by itself -- the cable that came in the original box with the player will work with the dock.

The only pins wired on the serial port are TX, RX, and Ground -- so turn off all hardware flow control when trying to talk to it.

It works fine as-is, and the player uses whatever the AC-power bitrate normally would be (115200 8N1). EDIT: requires Hijack, otherwise a docked player will assume DC-power and use a slower bitrate.

Cheers