Why does Apple TV not support Dolby Vision on a receiver using multiple HDMI outputs?

I have a similar but not exactly the same Denon receiver.

For mine, the signal drops to that supported by both outputs - so if Zone 1 supports Dolby Vision but Zone 2 doesn't, then Dolby Vision isn't sent to either. It is because it sends the same signal to both outputs.

Thus if you don't have a display on both outputs that has Dolby Vision, but you are splitting the same signal to the two outputs Dolby Digital will not be sent to either. It is the same for the likes of 4K, etc.

I’m using a Denon AVR-5960H and it supports both Dolby Vision and HDR10 with my Sony XR-65X90J TV. Works just fine.

The thing with Dolby Vision and HDR10 is the bandwidth requirements. You need to use HDMI cables certified for 48gbps and they’re not cheap. You also need to keep the total cabe length as short a possible. It’s not an Apple problem at all.

I'm not sure what you mean when you ask; "Why does Apple TV not support Dolby Vision...". On your Apple TV go to Settings > Video and Audio > Format > and within you'll find a list of several options to choose from for Dolby Vision, some specific for 4K televisions. Choose the option that best applies to your TV.

As for the receiver you'll need either to go online and check various receiver manufacturers or visit some brick and mortar outlets of your choosing. I don't believe anyone here offers shopping assistance.

I should also ask are you using high speed HDMI cables? If not upgrade your cables

Michail7711 wrote:

Yes, the cables are good.

The issue is having two HDMI outputs active at the same time. I have this setup to try and drive an LED sync box on the second output. It works great other than the ATV turns off Dolby Vision support and will only do HDR.

I've tried multiple receivers from different manufacturers. It happens on every one of them.

The current one I'm using provides nice detail on the HDMI output lines. Dolby Vision shows supported on both lines, 48 Gbps bandwidth, 4:4:4 chroma, while the ATV cuts off Dolby Vision.

If I don't use the LED box on the receiver the ATV will pass Dolby Vision. I can also chain the LED box in line with the ATV and pass Dolby Vision.

I don't use light boxes but if you are saying the light box might be causing the issue then perhaps you should contact the manufacturer for assistance. Maybe they can offer some insight as to how everything should be connected together.