Unless they have changes something the On/Off has nothing to do with the AppleTV, it would be for power connected devices via CEC so no need to have that button in the URC remote. The back button is the menu command from the older remotes.

the channel master remote may be worth the money to use to learn from if the home button actually functions as the home button on the Apple remote. And is so, how is it this code hasn't made it into the wild yet with so many looking for it for so long?