I just went outside to play around with my tri-zone entertainment... Put in a fresh copy of Christmas Vacation DVD.
Do you hear the DVD playing sound? The sound came right up for us...
To get a display, I had to hit AUX on the stereo just above the AC controls. Once I had a DVD menu up, I could see the DVD menu screen for my movie. I went into settings and there are several selections (like full screen or cinema) like you mentioned. There is also a selection called DISPLAY where you can set the brightness, etc. The top selection in that menu is ON/OFF. Mine had ON selection. Though, I put it on OFF, and the movie was still playing on the screen in the background. I ejected the DVD and put it back in and the screen was black, but for a brief moment, it did say that hit the "day/night" button on the NAV buttons to activate the screen. I did that, and the movie came back on the screen again.
All of this was with the accessories on but the engine off on the car. Either way, to answer your question, I was definitely watching the movie on the front screen. It worked all the way up until I put the car in Drive.
hope that helps!