I understand the WebRemote method and that would work, certainly. But, built-in seems more useful...
Client A ----------|
Client B ----------| ---- SERVER
Client C ----------|
Right now, any client can tell the server to play Song A. What about allowing clients to pass their requests through the server to other clients? So each client would see the server AND any client zones. So client C could tell client A to play Song A on its primary zone. Then, one could synchronize playback to all clients and get a house-wide media system going with fully independent clients, all operating independently so long as the server stays functional.