Question Overlapping moving music proximity problem

Google is only providing totally unrelated answers so turning here for help.

In my 3D scene:
There is a non-moving audio source playing music in a specific area radius.
There is also an audio source playing music attached to a roaming AI boss.
The problem is if the boss wanders into the area music zone, both overlap.

Please share the simplest solution that will disable or preferably gently fade out the area music when boss enters range, then re-enable the area music again whenever he leaves.

 

Probably audio mixer snapshots. One snapshot for the boss music, one snapshot for the regular tracks. When the boss enters a trigger area, trigger a snapshot transition (it has a fade duration and other settings).

See this Unity tutorial.