I think the default audio output of the Oppo Blu-ray is Dolby TrueHD and DTS-HD MastAudio and that requires an eARC (not Arc) connection to play the Dolby content and the Sonos Arc does not support DTS HD audio anyway, so the handshake is falling back to PCM stereo - so perhaps set the audio out to Bitstream, Dolby 5.1 or Dolby Digital Plus and see if that then makes a difference.

Hopefully the Denon, set to ‘pass through’ will work okay, but I’ve not taken a close look at that at this stage, as switching the Oppo to Bitstream/Dolby 5.1 etc. for it’s audio-output will (hopefully) sort the matter.

edit: you ‘might’ also need to power off/on the devices to get the ‘changed’ settings/handshake to be correctly recognised, but just see how it goes.

Thanks for the reply Ken. My audio output options on the Oppo are Auto, LPCM, Bitstream and Off. I tried Bitstream and powered everything off, but still only getting Stereo PCM on the Sonos. I’ve also tried Auto to no avail.

It definitely needs to be set to Bitstream, rather than Linear PCM, as you are not using HDMI-eARC - Are there any other audio-out settings to select either Dolby Digital 5.1 or Dolby Digital Plus? If not then go onto perhaps try bypassing the Denon Receiver temporarily and just see if the Player works when connected direct to one of the TV HDMI ports - if it does, then it might be the audio settings on the Denon Receiver …but one step at a time.

@HarvG 

Note, if you do see an audio-out choice between Dolby Digital 5.1 and Dolby Digital Plus within your sound-out settings, then try the latter first, but if no joy, then try Dolby Digital 5.1 instead, as we know from the connected Fire TV that that codec will work for sure.

If this is your TV make/model…

https://www.rtings.com/tv/reviews/lg/ef9500-oled

Then it looks like it will need to be Bitstream and Dolby Digital 5.1 that you need to select - I suspect that it will not pass-through Dolby Digital Plus through it’s ports. So that may save you some time testing that.

You may also find this device helpful (a bit later, when you do have everything working).

This (link below) is a combined switch/audio extractor, that would allow you to bypass your TV completely and allow you to get uncompressed LPCM/Dolby TrueHD Atmos audio from your Denon Receiver and Blu-ray Player and compressed DD+ Atmos audio from your FireTV 4K…

https://feintech.eu/en/products/feintech-vax04101-hdmi-earc-pass-switch-4x1

So I’ll just post that here for you to maybe look at, at some later stage.

It’s definitely set to Bitstream. The only audio setting that has DD 5.1 as an option is for S/PDIF, which would not seem to impact the audio out on HDMI. I did nonetheless set S/PDIF to DD 5.1, but no change to the Sonos. I previously had the Oppo connected directly to the TV, and same result - Stereo PCM on the Sonos.

That is my LG TV - but again, the Oppo is only allowing me to select Bitstream for audio output and no DD 5.1 option.

Thanks!

Hmm ? …may just need to locate its user manual somewhere online (hopefully) and see what it says - and see if it does support Dolby 5.1 out over its HDMI connection?

Does the Denon Receiver have an S/PDiF audio input that you could perhaps try in the meantime?

@HarvG When you get Dolby Digital audio from the Fire TV Stick, is it connected to the receiver or directly connected to the TV?

Is Downmix Mode on the Oppo set to 7.1 or 5.1?

What specific Blu-ray disc are you testing?

Sorry it got late so had to sleep, anyhow I found the user manual and so just looking at it now:

Link below:

http://download.oppodigital.com/UDP203/UDP-203_USER_MANUAL_ENGLISH_V1.0.pdf

@HarvG,

Note the HDMI cable should be connected to the ‘main’ port and not the one marked ‘audio’ (mentioned just in case) (page 13)

Also as @GuitarSuperstar mentions - select to downmix the audio to 5.1 (page 15 & 64)

Leave the HDMI audio output set to Bitstream (as mentioned earlier) (page 56)

Note Dolby Digital Plus is supported by the Sonos Arc, but I’m fairly sure from what I read earlier, that the TV will only pass through a Dolby Digital 5.1 signal, so I assume you will get the DD5.1 codec when you make the changes mentioned. 

I can’t see anywhere where it lets you select DD5.1 but choosing Bitstream should hopefully work, aswell as changing the downmix mode

I would also perhaps begin by connecting the Oppo direct to the TV as you have connected the Arc to the TV and simply cut out the Denon Receiver in the middle if you do have enough HDMI ports available on the TV to do that.

Downmix Mode set to 5.1. I’ve been using  “The Batman” and “The Guardians of the Galaxy Vol. 2”.

Thanks

HDMI main and not HDMI audio - yes.

Downmix to 5.1 - yes.

HDMI audio output to Bitstream - yes.

I had already tried the Oppo connected to the TV directly and got the same results - Stereo PCM on the Sonos.

I do not have enough HDMI ports on the LG to keep the Oppo connected directly. I only have 3 HDMI in ports: the ARC HDMI one for the Sonos, another for the Amazon Fire Stick, and the third for the Denon, which feeds the Oppo to the TV. If I go back connecting the Oppo directly to the LG, then I cannot keep the Denon connected.

I would perhaps leave the Denon out the mix ‘temporarily’ to begin with, to get the Blu-ray setup and working first of all with the TV/Arc - as we know that the TV will pass-through the DD 5.1 audio to the Arc. 

Having put the mentioned settings in place on the Oppo with it connected to the TV, did you go onto try powering off all the devices for a minute or so, just to get them to setup the correct handshake again? Then play something that has DD 5.1 or even DTS 5.1 (not DTS-X or HD) audio and see if that may work for you. 

Just reconnected the Oppo directly to the LG, powered everything down for a few mins, and still same result - Sonos is getting only Stereo PCM. So the conflict is somewhere between the Oppo, the LG, and the Sonos.

If the Fire TV is working when connected to the TV, it points to the Oppo being the issue - a setting we’re missing perhaps?
 

Just curious, but does the Fire TV give you DD5.1 output when connecting that via the Denon Receiver set to pass-through the audio?

I’ve just come across this in the user-manual (page 57):

Can you switch the DVD-Audio Mode to ‘DVD-Video’ and see if that makes a difference.

I’ve just come across this in the user-manual (page 57):

Can you switch the DVD-Audio Mode to ‘DVD-Video’ and see if that makes a difference.

Already had that set to DVD-Video - no change.

Would it make any sense to connect the Oppo directly to the Sonos to see how the sound is processed, or is that not practical/feasible?

I’ve just come across this in the user-manual (page 57):

Can you switch the DVD-Audio Mode to ‘DVD-Video’ and see if that makes a difference.

Already had that set to DVD-Video - no change.

 

Would it make any sense to connect the Oppo directly to the Sonos to see how the sound is processed, or is that not practical/feasible?

 

Yes it won’t hurt to try that and see what audio format you get - if it’s still stereo, my thoughts are to perhaps also try a different HDMI cable.

I’ve just come across this in the user-manual (page 57):

Can you switch the DVD-Audio Mode to ‘DVD-Video’ and see if that makes a difference.

Already had that set to DVD-Video - no change.

 

Would it make any sense to connect the Oppo directly to the Sonos to see how the sound is processed, or is that not practical/feasible?

 

Yes it won’t hurt to try that and see what audio format you get - if it’s still stereo, my thoughts are to perhaps also try a different HDMI cable.

Connecting the Oppo directly to the Sonos via HDMI resulted in no sound.  Will have to consider a new cable, but the cable I’m currently using is successfully passing a 4K HDR video signal to the LG.

The Oppo doesn't put out an ARC signal, so it's never going to work connected directly to the Arc.

@HarvG 
Ah yes of course jgatie is right, (how stupid I am‍♂️)… you need to return the audio to the Arc over an HDMI-ARC connection, but you could use the optical-to-HDMI adapter (that came with your Arc) plugged into the Oppo, but that really somewhat defeats the object of what we were trying to discover and that’s if the audio-out over its HDMI connection is Stereo, or Dolby Digital 5.1

Anyhow, you may aswell try it with the Optical-to-HDMI adapter and see what audio you get from that port. It may at least show the audio out settings are correct even if it’s going through a different port.