Worked for me. I hadn't noticed that Apple TV wasn't showing in my iTunes library. (it wasn't so thanks for pointing that out.) So first I rebooted ATV, it said it had an update - I updated it. Then I went to settings > computers > told it to sync with my <username> library. It generated a 5 digit code. Then I went back to my computer - and iTunes told me to enter the code - and that was that. Now all my media is there (which it was before), I'll just have to be sure it actually syncs when/if I make any changes.
JUST NOTICED. IT'S NOT LISTED UNDER DEVICES. So I can play things that are all ready on it, but it doesn't seem to be syncing or recognized as a device by iTunes???