A couple of differences of Sonos vs. Apple TV:
- Sonos is sound only. No need to have a screen handy in all rooms you just want sound.
- Sonos can use a NAS - this will be shared between the different Sonos units. No need to have a full computer running, or a hard drive in the device Moving parts = noise and heat. I don't want an AppleTV in my bed room.
- Sonos supports Internet radio.
- One of the Sonos devices has an integraded, good quality amplifier. Just hook up a couple of speakers, and you're done. AppleTV is just a signal source for a receiver or similar.
- Sonos can sync sound across units, e.g. for parties.
I've got an AppleTV and use it as my primary sound source connected to my Denon/B&W setup, and I'm happy with it... but I'd love an improved Sonos too.
For AppleTV I want 96/24 support, a SDK, spotify support, NAS support, internet radio, optional hard drive and a version with an amplifier in it. And a more complicated remote control - the current one is too simple, so things like power off doesn't work.
For Sonos, I want 96/24, Genius and spotify support. If they add that, I'll buy it and find a way to make Itunes put all its file on a NAS.