I just purchased a 2006 E350 that has the comand navigation unit. I was told that this system needs something to make the navigation work. Is it just the nav DVD? Also, is there a good place that can install a dvd player / TV tuner, and monitors in the headrest in bay area, cal? Can the front dash unit also be used as a screen for video? Is there a software update that will allow me to see the detailed music information from radio stations songs or which cd's are playing?

Thanks