Have a look at Airfoil which allows you to capture any applications sound output, e.g. Squeeze or iTunes, and send it to any airport express with individual volume control. Airfoil can be controlled via indigo or any other app that allows remote applescript execution (dont know about windows). Use it my house and works a treat. IF you want to be really sophisticated you can VM up multiple iTunes servers or have >1 AppleTV (or using Squeeze to multiple players etc) and then with a modicom of javascript you can have different sources in each room playing or all rooms playing the same source or any combination thereof.......using ProntoTunes you can connect to each source and change its speaker output from the Pronto if you want to do it realtime and can't be bothered with Javascript.