ccjw.
Having found any other fix to watch DVDs. There is a "soft fix" so that you can input Destination information while driving. It also allows you to use the phone. Not sure about the MP3 part as haven't tested that with the soft fix.
Soft fix is: Go to menu screen, select volume, tap the screen in the top LHS then bottom LHS, then again top LHS and bottom LHS of the screen.
This brings up a service screen. Press and hold the Override setting for about 5 seconds and setting will change. Return to previous screens. This will last till you stop the car.