Set volume for background audio to custom level

We use background audio behind our song slides as well as before/after the service (or also during communion).
It would be useful to be able to set a custom volume for the background audio so that when the cue is launched no adjustment needs to be done to the volume. Similar to what is available for videos. At a few services I have no one at the PA mixing desk and so this facility is very helpful.

A bonus would be to have the option for a song to fade out when the cue is finished.

A further bonus would be being able to control the volume of the program remotely from the phone/tablet app.

This is a feature I need as well. Small, older congregation so now one at the back with the sound mixer. Fade out would be fantastic