Samsung QLED Q8-Samsung K850 Soundbar compatibility

I have a...

Samsung QLED (Q8) 55 inch TV.

Samsung K850 soundbar

Apple TV 4K

Running Belkin Dolby vision HDMI cable into soundbar. Running Audioquest Cinnamon to TV for "ARC"

Should I be using 4K "HDR or SDR" format? As well as both Match Contents turned "ON"?

Dolby Atmos works great. Everything looks great when I'm watching "HDR" on Netflix. However "Ultra HD" 4K looks very poor. Furthermore I can't even select "4K SDR" on the 4K Apple TV if I have the Samsung TV "UHD" selected. Please advise.