Originally Posted by didadi
I can confirm it does play 5 channel audio. The way I confirmed is, kodi has this option
of 2.1 or 5.1 - native encoding for audio. I had left it as it is, and I played a movie that
had 5.1 encoding. I was able to hear much better sound. I now wonder if it's Dolby
audio, does TV show the status that it's Dolby audio signal being output somewhere
like Dolby HDR?
Yes the TV can play 5.1, via HDMI ARC. The computer can play 5.1 also, if I hook the receiver to it first, but then I cannot pass through 4K HDR or DV. I can play files with 5-channel audio via the TV's USB port using the Roku media player app.  Actually, I think stereo is all that roku can play properly.[/edit]
What I was trying to do was pass a video with 5.1 audio directly to the TV from the computer.
PC Windows 10 -> GTX 1050 Ti graphics card -> HDMI 1 -> TV -> HDMI ARC -> Pioneer VSX 521K receiver.
I found my problem.
First I found this Settings -> TV Input -> (MY PC Input) -> There is an option for HDMI 2.0 that must be selected!! I think mine was originally on auto or HDMI 1.4, but once I selected HDMI 2, I had no trouble getting HDR on my computer input.
Further receiver does not have HDMI 2 for pass-through of HDR to the TV, so I had to split the audio and video as follows: Hope this makes sense.
1.a Configure Primary display in Nvidia Control Panel to 4k x 2k (recommended), Refresh rate 60
1.b Chose to use Nvidia color settings
1.c Set Color Format to YCbCr422 and click the apply button
1.d Set color depth to 10bit and click the apply button
1. e Check that TV Settings -> HDMI Input for computer is set to HDMI 2 or higher
2. Turn on HDR in Windows Display Settings
3. Plug in receiver in DVI port on Nvidia GTX 1050 card (using DVI to HDMI converter)
4. Windows Display Settings -> set up receiver as second display with 720p
5. Configure Windows Sound Playback so that receiver is default device. Click Config button and Test speakers are shown and work.
6. Turn off audio for TV on Nvidia Control Panel. Check that receiver shows as an audio device in same settings page.