You can do that, sort of. Look at the .url file handling — that’s nothing more than a pointer to a shoutcast style stream.
So yeah, you can do that, but the location of the URL is sent at the time the client connects, not when the user selects the stream.
What I’m saying is that when the client connects to the daap server, it feeds it the urls for all streaming resources.
Of course, that could be a pointer to a http stream that redirected somewhere else, but it wouldn’t be done on the daap side.