Or is it 1 app at a time?

Yes. Just start playing your music and then go into the Nav app of your choice. The Voice guidance will slightly mute the music when it tells you to turn.

Or if playing the radio, once the sat nav app starts up, double click the home button and then select MIX radio.

On many models, such as my X950BH you have an information bar at the bottom of the navigation screen that can show the song playing or the street information. With mine I can play videos, MP3 songs or the radio and switch between screens easily.

Alright, thanks for the info! Might be time to upgrade my Z130BT.

Also I shd add my comment referred to the app radio 2