Surround vs Stereo setting - reversed on DirectTV Stream box?

How is the DirecTV Stream box connected to your AV Receiver?

What brand/model AV Receiver?

Do you have other sources connected to the AV Receiver?

HDMI 2.1 connection direct from Stream box to AVR cbl/stb port.

Onkyo TX-NR5100

Yes, Xbox One X- direct connection to AVR.

TV is direct connection to AVR main port 

Does your Onkyo provide a display or menu showing the input audio characteristics, e.g. DD 5.1 or PCM 2.0 audio?

I have seen the same behavior on my McIntosh MX-121. When i surround there is no center channel but just left/right. In stereo all my Surround lights show active.

@MacGuy ,

Are you using a DirecTV Stream (C71K) box?

All my speakers show up in stereo mode too.

@Poleaxed 

But are you actually getting DD5.1 surround audio?  Or is your AV Receiver simply processing the stereo signal into a surround output?

I think litzdog has the answer here. If you feed the AV receiver a stereo signal but select "surround", it will process the signal into a pseudo-surround which will output to all your speakers. You need to read the user guide to your AVR to see what each of the selections actually do.

I think that it's just specific content that will output 5.1 and some just stereo.  It is possible that my AVR is upmixing the stereo but I am not totally sure what the behavior is.  Right now I have switched to surround and will just continue to test.