Brainstorming along this line there are some possibilities that might be available with Bluetooth.
I have a MACBOOK w/ XP + Bluetooth downstairs for work, and a newer PC with Bluetooth upstairs. I notice that with the new version, Bluetooth stereo is available, and that both computers at least recognize each other.
Both units can send and receive, WILAN and BT. It might be a bit involved, but worth a try