It would enable volume levels
- louder than the maximum android setting with a "pre volume" set to high
- softer than the minimum android setting with a "pre volume" set to low

I know that the first point has already been requested. What I am really interested in is the second point.
I usually listen to podcast at work, in a very quiet environment where the minimum volume setting is still too loud. I guess there is an impedance matching problem with my headphones which could be solved by buying new ones, but I would like a software solution.