Thanks! Behind the scenes, I've written an node.js component that's able to talk to OS X/iOS devices (https://github.com/stephen/nodetunes) via AirTunes and stream in raw audio data. From there, AirSonos converts the audio into a "radio" stream that Sonos can understand.

The code is still very much 'alpha-stage' at the moment; functional but not completely consistent yet. I'm planning on doing a writeup with further progress!