Getting back to the OP, as for the picture on the X800. While playing a 4K disc, check the input signal on the Denon. If you are not seeing 4:4:4 but are seeing 4:2:2 or 4:2:0, there is a setting off somewhere in the chain. If you have Enhanced activated in the Denon, check the TV settings for anything like UHD Color Setting. In the regular picture settings, see if colors are set to anything like auto, custom or native and play with that setting. Check all of the Screen settings in the X800. Leaving everything at Auto should be fine. Custom picture settings can be fun to tinker with but you should not feel like you have to because the picture sucks. It would only looked washed out on 4K HDR discs if, somewhere in the chain, a setting is off. I've had this issue myself and was able to remedy it with a TV setting. Not all HDR capable TVs and devices are created equally. Check the supported resolutions on all of your devices. It does matter. I hope you work it out. If it all checks out and you just like your custom settings, enjoy.