How do you get the unit to play DVD's while the car is movin

I have a follow up question...

I want to connect an external DVD player to my RNS-E via the tuner and all the Dietz adapters (1417 and 1280 if i remember it right) .

The plan is to have it in the glove comp, now finally the question...

How do I make it possible to play Audio CD's in the DVD player and listen to it from the RNS-E?