Enter the Airport Express I had sitting in my pile of networking junk. I connected the Apple TV and the Airport Express over Ethernet, configured the Airport as an Airplay device, configured the Apple TV to use it, and, presto, analog sound. Without any noticeably delay, even.
A few notes:
- The Apple TV can run either WiFi or Ethernet, but not both concurrently.
- The Airport Express can be configured in Bridge Mode, and you can connect the second Ethernet port to your LAN. Doesn't matter which port is connected to the LAN and which is connected to the Apple TV.
- Alternatively, you can set up the WiFi on the Airport Express to "Extend Network" and connect the Apple TV and Airport Express to the rest of your network that way.
- The Ethernet ports on both the Airport Express and Apple TV are only 10/100 ports, so that's the highest speed you'll see on that link. Should be plenty for most applications.