I set up a brand new out of the box Roku Ultra running through a Pioneer Elite receiver with a Samsung display. After set up, the audio only outputs in stereo regardless of the application (YouTube TV, Netflix, Disney+, and Hulu). I confirmed that the Audio mode is not in Night or Leveling Mode and tried multiple HDMI ports/cables from the Roku into the receiver. It seems like this is an intermittent problem with Roku's, but I have not found any recent threads (< 6 mo old) on this topic. Has someone experienced this issue and was able to fix it without some series of good luck and/or voodoo?
As a follow up, I am running a Roku 4670 through a Pioneer Elite VSX-90 with a Samsung 8 series display. The Pioneer is capable up to Dolby Atmos and does not even show the Center and Rear channels on the display even in the Roku menu.
I just set up a Roku Premiere and am having the exact same issue. Everything plays in stereo, not in 5.1. My Roku is connected via hdmi to my audio receiver, which is then connected to my tv via hdmi. Everything else that is connected in the same exact way (ps4 and cable box) work perfectly.