Ideally you'd wire connections directly from the docking unit to the RCA terminals on the back of your case. If you don't have an extra harness you don't mind modifying, then the best thing you can do is to use some adapters for the connection.

Since I don't plan on using a tuner module, I think I'm going to end up using some of its pins on the harness. I'll fit them with new wire (a delicate matter) and transplant them into the correct sockets for the audio (that part's easy).

Bruno