DVD drive has region coding, as stated before. And besides, every factory option that puts TV or DVD movies on the idrie display (CID) has to be blocked when the car moves.

So, you'd have to flash the drive with firmware from the internet to get it region free and have to find a module that blocks the speed signal, so that you can see something on the screen while the car is in motion.

The individual system for the rear is very expensive...

I just bought a portable DVD player that I can put on the passenger sunblind and play the sound through the AUX input.