Connecting Two Analog Sources to One Analog Sink
Your CP probably does have an AUX input, but it's hiding as the CD changer control plug.

You can reverse-engineer that. In fact, a solid 12 seconds on google revealed this gem from http://nodivisions.com/tech/kenwood_aux_adapter/:



With that, you can simply select the CD changer as audio input to the CP and be done with it.