Multiple a2dp streams seperate volume possible?

Hey all I have a note 4 phone and while in the car I stream my audio via Bluetooth ,a2dp, also I use navigon navigation that stream the directions also by a2dp. Wondering how I can set the volume for navigation lower than the music? While navigation is active the Music mutes then the navigation directions come through, but its to loud and I would like to quite them down but the volume buttons also turn down the music, Any ideas??