I dont have the system but i think i know the answer
You nead to switch to AV channel on your nav screen and then you will heare the sound on the speekers. (This will only work it the dvd is connected to your tuner in the trunk or if connected to the av input below the vents for back seat) If you want Tv in motion you will nead to buy some kind of tv in motion adapter.
You should read this too http://www.xoutpost.com/articles/x5/e...nt-system.html