Well, this only works with the RoKu soundbridges, and they do some black magic to pull it off.
There are a lot of DAAP client implementations out there, and they would work very well with firefly.
Just take a look at the DAAP code in banshee, rhythmbox or the winamp-daap plugin for instance. Of course there are also all sorts of DAAP bindings for various languages, all of which are more or less incomplete, but deffo better than starting from scratch 😉