I haven't found an option either. Personally I think they should make like 9 radio like buttons with the icons of the audio apps. Sometimes some of AA's screens can be laid out better.
Like why not replace that "Exit back to Mylink" with a Play/Pause button for whatever audio app you last used. It really irks me that I get in my car and connect up AA - of course I want whatever audio I was playing to start playing but nooooo. I often see the Now like card come up with "Directions to so and so" and hit that. Now maps covers the screen and I have to go back to the audio section to hit play then back to maps. It would be so much better if it would simply start playing on connect or at least have a play/pause button available at all times.