I see your problem. Your receiver is a step up from mine being compatible with 4K but audio wise, it's the same and not compatible with Dolby Atmos.
All streaming devices I have will output in Dolby Atmos while outputting a 4K video. So you have to setup in your streaming device's audio setting...
I had a Samsung 55RU8000 and it's HDMI inputs would not work with my Denon's AVR-2312ci. In my case it was OK because the Samsung TVs performance was so terrible, I was returning it anyhow. But HDMI incompatibility issues are still out there apparently. With LG being a much better company than...