First, find out what driver version(s) you have installed. Go to
System Preferences -> Sound -> select the Output tab. Look at the list
of the sound output devices.
If you see “AirBeamTV Audio”, you have
the audio driver version 2. To uninstall it, you need to ...
This is obviously not supported and I don't know what wackiness may result from it, (some weird stuff happened when I did it myself) but this is where you find and put the SDK's for specific platforms in an Xcode version.
On the new Xcode (the one with the SDK that supports your device/OS/etc.) you can find the SDK bundle itself in
As of June 2019, iMovie Theater is no longer supported and people are being moved to using iCloud Photos instead.
That being said, it appears that there is no way to add an additional account to the 3rd generation Apple TV, only the one iCloud account is allowed and thus only one iMovie Theater account can be used at a time. If you want to switch, you need ...