Separate volume control is what I'd call an essential upgrade for this kind of app.
The volume difference between 0 bars and 1 bar is often enormous, giving you a choice between completely muted, or too loud to be able to safely hear any background noise in your home environment... (like if someone is about to enter the room or calling for your attention)
Given that the app is for watching porn and masturbating while not being able to SEE anyone entering the room, being able to still hear it before it happens is potentially quite important to avoid embarrassment.
In Heresphere. you can set the system audio volume to one bar, and then adjust the volume WITHIN the app to use anywhere between 0-100% of that one bar. I'm not a programmer, but it seems like this shouldn't be a complicated thing to implement.