I've looked here Reduce minimum
and here Minimum volume too loud
And did not find a solution to this issue - minimum volume on my bluetooth headset paired with my iPhone is too loud when listening to streaming app like Pandora.
One limited solution that should work with wired or wireless headsets - if you listen with just one earpiece:
In settings select: 1. General/Accessibility 2. Scroll down to Audio Volume Balance slider. 3. Move it towards the ear piece that is NOT in your ear. I.e. if you have only the right ear piece in your ear, move the slider towards the left. This will reduce volume in the right ear BELOW the minimum that you can achieve with the regular volume control. Which proves it's possible and why on earth Apple doesn't allow you to lower both channels this way I don't know. 4. May want to enable Mono Audio as well.
Not a solution for hi-fi listening but works well enough for having some casual background music without sacrificing your ear drums.
Has anyone come up with a solution for lowering volume in both ears for streaming audio apps over bluetooth headsets since the other threads were closed?