On a whim, I replaced a dead Airport Express that fed optical out to my (pre-airplay) Zeppelin in my bedroom with an Apple TV2. Except for setup, I don't have it attached to a TV. Nevertheless, the functionality blows the AE out of the water. Optical out is 48kHz only, but it sounds perfectly fine in conjunction with my Zeppelin. This allows me, using an iPod touch or iPad with Apple's Remote.app, to play music from my library on my main server.
Although most normal human beings would also attach this to a TV via HDMI, I just wanted to make clear that as a zone music player, this thing works really well. It will kill Sonos.