Currently I play out with my Denon gear but also Rekordbox. I manage my music library in iTunes with smart playlists, since it’s platform-agnostic. In Rekordbox, I can simply sync my iTunes playlists directly to my USB drive. In Engine, I can import the playlists but not sync them - any additional changes to the playlists require deleting and re-creating the playlists in Engine.
Fixing this would really save time for me, since every time I download new music I need to delete and re-add 15-20 playlists to sync my USB.