Just wanted to share my story of getting the stars aligned to get HDR to work. I thought that this may help someone else. I decided that I was going to go all in on the 4K HDR, so I purchased a Vizio M55-E0 4K TV that has HDMI 2.0a/HDCP 2.2, HDR10 and Dolby Digital. I also purchased the Sony STR-DN1070, a 4K HDR AV Receiver with HDMI 2.0a/HDCP 2.2, HDR10 and Dolby Digital. Of course, I have 4K HDR HDMI 2.0a/HDCP 2.2 compliant cables. What I discovered is that each device has at least one setting that has to be correct, for all the stars to align for HDR. The TV only has one HDMI port that is HDMI 2.0a compatible and you have to set the input for that HDMI 1 port to "FULL UHD Color". You have to set the Picture Mode to "Computer", to enable the 4:2:2 color option for the AppleTV. The receiver was easier, since all the HDMI inputs are HDMI 2.0a/HDCP 2.2 compatible. It just had two settings to change for the magic to happen. The HDMI signal for the input had to be changed from Standard to Enhanced and CEC had to be turned on for the switching of the video signal. With those two devices set, the AppleTV 4K could change the Chroma from 4:2:0 to 4:2:2. Once I had all those settings correct, it allowed it to detect the TV as HDR compliant and do 4K HDR at 60hz. I didn't think that it would take this much effort and research.