I use Musicolet Pro for offline playing on my T93 and the Media Control Widget works fine with it once I start playing. It’s only if I need to browse through the folders/playlists/songs that I need to exit DMD  app and go into the actual player, then go back to DMD when done – I don’t know if it’s possible to change this behavior and bring up the media player’s browser directly on top of the DMD app or inside a container of some sort. Musicolet is one of the most popular Android offline media players and so feature rich.