Audio setup for Macbook and XBox? I have a one set of speakers, 2 macbooks (girlfriend and I), an iPod touch and a XBox.

Now, I struggle with the audio because anytime I want to listen music or use the xbox, I have to switch the RCA cables plugged into the speakers.

It seems that Airport Express could be a solution and airplay seems really nice, but I don't know how/if it will work with the XBox?

Do you see a solution to simplify that situation?
You are right that the AirPort Express would work for the iPod and Macs. It won't, however, work with the Xbox. For that, I recommend getting a little RCA switch and RCA-minijack adapter. Using the adapter, plug the AirPort's audio out into one of the input ports of the switch. Plug the Xbox another input port. Plug the speakers into the switch's output end.

When the switch is set to the AirPort's input, you can AirPlay music. When the switch is set to the Xbox's input, you'll hear sound from your Xbox.