Welcome to the community.
First off, ME was designed to stop all play when returning to the home screen. You can do everything else while still listening to music, except for video (obviously) if you follow the next steps. At the music player screen, click on the submenu button to bring up the submenu, on the far right will be the GPS button that will bring you to your NAV program without stopping the music, the screen will even auto adjust to still have the audio buttons on the left. In the music player submenu, you can click on the browse button to browse your media folder while still playing music as well as using your external apps too.
If you do not see any of these buttons, it is possible that they were omitted when that particular skin was created although that area of the submenu still contains that functinality.
Hope this sheds some light.