Hello ... I've seen a couple of threads that point to this problem, but can't quite see if there's a solution???
I am using my new Samsung S5 for 2 functions while driving. (1.) I listen to an audiobook (audible) and (2.) I run, when needed, MapFactor Navigator for SatNav directions.
The problem: the Navigator directions are spoken so loudly that the bluetooth loud speaker actually grumbles (and it does send shivers down my spine), but the only way I can see to control the volume for the directions is by turning down the media volume with the result that I can no longer hear the audio book. The instructions are spoken on top of the audiobook narrative. I also use RunKeeper where the volume for audio cues is loud but not as loud as Navigator and there is a feature called "audio ducking" that pauses the audiobook narration when cues are given.
I could live (possibly) with no verbal instructions (just following the visual map) ... not good, but better than busting my speakers and my ear drums and drowning out the narration for my audiobook. But I can't even find a way to mute the driving instructions. Will look around, perhaps one of the other SatNav apps have taken multiple source listening into account.