Just a wacky idea but Apple tv has the couch surfer option? I have only heard haven't pick one up yet. But when the iPhone came out there was a lot of talk about orbcast and setting up the stream to be heard over the net for either XM or Sirius. So if couch surfing is an option this maybe viable.
That Apple tv usb hack sounds promising. This might also be a viable option.
There is a work around. I use AirFoil and you can stream music to Airport Express units or the Apple TV. I use StarPlyr on my desktop, open up Airfoil and then send music to any of my Airport Express devices or the Apple TV. I have the Airport Express connected to Tivoli's. I have a small house, so really haven't gotten the real power of this solution. It's basically a low-cost, low-feature edition of Sonos -- but it streams Howard to three locations, so I'm happy with it.