If you're using ISA routes and have different service routes for your various lines of business, I think you can you can specify a different music route for each service route. This should also apply to COT routes as well and play different music sources to different types of external callers.
If I'm not mistaken, the music source specified in the CDB is used for internal MOH once a music route is provisioned against trunk routes. If no MRT is on the routes, then everyone hears the same single MOH.