I’m not sure if this is a limitation of iTunes or Firefly, but I have finally setup my large share with Firefly successfully, and managed to get iTunes to load the database and stream the music (albeit sluggishly, loading a 400gb database of music eats over 100mb of RAM, nearly 200mb peak!).
My only pitfall which is what I originally intended to use Firefly for, was to allow guests to copy the music from the server into their own iTunes libraries for playback.
I’m not sure if this requires a copyright bit to be turned off.
Any help is appreciated ๐