The code samples we have shown on our demo stands and which are included with the WebBrick Gateway development kit control iTunes devices, typically a computer running iTunes, where we show someone answering a voip phonecall & the iTunes player being automatically paused, and upon hang-up, the iTunes player restarts playing. This is achieved by having the Asterisk/Trixbox PBX used send in the published HTTP strings to the iTunes player.
This technique can be extended for a number of audio devices, but we don't expect to write all such support ourselves, but rather will respond to the market needs as given to us by Installer partners such as yourselves. You also can move ahead on these without further help from us, if you need to. The system is completely extensible.
We have a lot more plans for audio & video, and yet the opportunity to change those, so please do tell us what you need and when you need it. (These sorts of discussions will likely progress outside this public forum.)