Guys,
I'm afraid that you're all barking up the wrong tree here. Trust me, I've done this, and do it for a living every day. Even if you the xbox's were to somehow sync up what they are playing, you still wouldn't have perfectly in sync music with the method you're proposing. The reason is that different receivers take different amounts of time in milliseconds to output their audio. Try it some time. You can take two different receivers, put them both on the same radio station, and more often than not you'll have a very slight, but noticable, difference in the output.
The method that will definately work, and is better anyway, is to have one centralized xbox that outputs to a multi channel amp, which then ties in to ceiling speakers in different rooms. This is basic distributed audio 101 here, guys. I'm actually setting this up myself.
Controlling this in other rooms is where things get more tricky, but it's not really all that challenging when break it down.
You'll want a volume knob in each room that is wired in between the amp and the speaker. This will allow you to set different volume levels in each room. For most of you this is all you will need. Most people only want multi-zone audio for parties and such and don't mind controlling their playlist from a central location where the xbox lives.
For anyone else that DOES want control in each room, you've got a couple options. First off, the easiest solution is to have some sort of computer in each room where you can control the xbox from the web interface. Done deal.
Secondly, (and what I'm going with) is to use some sort of TV or tiny wall-mounted monitor in each room that is wired to the video ouptut of the xbox. This allows you to have full display. Then, for control you'll want a wall-mounted universal remote such as a RTI RKM-1 found here
http://www.rticorp.com/products/rkm1.html or, way more expensinve
http://www.universalremote.com/product_d...?model=136
Anyone that has any questions at all I will be glad to help. I do this shit every day
