Aftermarket Navi

Hi everyone....I am a new to these forums so bare with me. I'm about 95% from purchasing a Tahoe and I had a quick question. The model that I am getting has no navi but it does have the dvd player for the back. My question is...if I purchase an aftermarket navi system, how do you get the dvd player to work in the back? The factory headunit comes with 2 slots...a slot for the dvd and a slot for the cd so I was confused on how you would get the dvd player in the back to work with an aftermarket one.

Sorry if this is a simple question and thanks for any help in advance!

Welcome.....If the aftermarket nav you use has a video out than you can feed that to the overhead or whatever rear seat entertainment you have. You will need a interface to retain onstar and other features such as door chimes. There is a plug and play harness that plugs into the RSE wires giving you rca in's and out's......hope this helps