The simple use case is to have the mp3 currently played by my Soundbridge to be fed from the Firefly server also to my Apple Airport Express and thus have the same music all over the house.
The only controls needed would be a tick-box (on) and perhaps a delay adjustment parameter in the web interface.
I haven’t yet looked into the Airtunes protocol itself. Merely concluded that the player already exists at raop-play.sourceforge.net.