Hi - Trying to get the external drive as primary. Going through the steps it asks to select the drive (although I don’t recall seeing the message about it being formatted and erased) and then takes some time to copy the data. When I run iTunes it asks me to register the ATV and the capacity shows 144gb as other (Orange).
On ATV - Settings -> General -> About also indicate the internal still being used.
Have turned the device off and on.