Please see my more in-depth answer in the thread linked below. A direct answer to your question is the Apple TV does not support Atmos contained in a TrueHD audio codec (which is what just about every Blu-ray with Atmos uses)
Please see my more in-depth answer in the thread linked below. A direct answer to your question is the Apple TV does not support Atmos contained in a TrueHD audio codec (which is what just about every Blu-ray with Atmos uses)