Easy ....
1. Choose High Profile
2. Turn off Detelecine
3. Set to Strict Anamorphic in Picture settings
4. Hit the "+" Button in the Presets Drawer
5. Type "AppleTV 3" for a Preset Name
6. Set Use Picture Size: Source Maximum
7. Check "Use Picture Filters"
8. Click Add.
... at least until hb releases an atv3 preset. Which will pretty much be this barring a couple minor changes at most..
What about audio settings? In particular for music. Just increase the bitrate, or is there anything else that needs to be done to get the best sound?