Many best double din head unit today have very user-friendly function such as the Dual Zone function. Usually it's in the all-in-one Car DVD/GPS unit. What does it really mean? Let me tell you, usually it has 2 meanings:
1. Enjoy Car Navigation with car speakers in the front zone; while passengers in the rear can enjoy DVD movies through the AV output of the unit.
When you're navigating in the front, your customers will get boring since it's non of their business. Can they also have some entertainment in the back seat, watch some movies or listen to some music from the headrest monitors? Sure if your car dvd player has such function, they will get much more delighted. Just install a pair of headrest monitors in the back, and connect it to the Car DVD, then your wife, or your girl friend, or your kid will get highly satisfied. And all of you will have a happy journey no matter it's long or not.