This is a rather minor request. If it's at all possible for the music player to respect the Jukebox/Note blocks, or, have it's own slider to fine tune the music volume. It only respects the master volume slider.

I understand if this is perhaps a limit on the mod itself.

Also, would it be possible to somehow stop the normal background music from overlapping or playing while the music player is running?

There should be an option to change the music player volume settings in the mod options, in position named Base settings and it starts at 30% of volume. It was originally tied to Jukebox volume, but I decided to make it a separate option.

Please note, changing that option while a song is already playing won't have an effect until another one starts playing.

About stopping the background music, it's something I want to do but it seems like there's no obvious, easy way to do it. Because of that, I'll leave that issue open for now.