Can I just ask what router you are using here?… Also are you now seeing the surround audio ‘badge’ on the Sonos App ‘Now Playing’ screen when outputting a TV Show/Movie with surround audio? (Similar to the attached).

Hello
I am using a Fortinet D60 with Forti Access Points.

When I had the system on Wifi only, I got Stereo PCM when playing Netflix or any other linear TV. I also had problems reaching the Sub 4 from the app. Many times it just was “lost” from the app, and I had to reset the device and connect it again. 

I got Dolby Digital 5.1 when playing BlueRay, but there was no sound from either the sub or the Era speakers. 

After I added an ethernet cable to the Arc Ultra (arc ultra and sub are now on the same switch), all components are working and the badge in Sonos app is now showing “Dolby Digital” when I play (new) content on Netflix and linear TV. 

I have not performed a router reboot during this period.

With regards to PCM 2.0 Stereo/Dolby Surround Sound, it shouldn’t make a difference if the soundbar is wired to your network, or operating over a WiFi connection, as that audio is received over the HDMI input to the soundbar - if you were not getting audio from the surrounds & sub over WiFi that ‘usually’ indicates the soundbar is wired with the WiFi adapters switched ‘off’ in the Sonos App - you need to leave a soundbar WiFi enabled, even when it’s wired to the LAN as the surrounds and sub link to the primary HT device over an ad-hoc 5Ghz (fast) wireless connection. The Surrounds & Sub also get their IP addresses, by proxy, from the router, through the Soundbar primary device. The alternative is to cable everything back to the router/switch.

Thanks for your reply.

I agree that it should not make any difference if the soundbar is wired or connected to wifi. I started out with wifi only, but had to put the sub on ethernet to get it to stay present in the sonos app. I thought it was something wrong with the sub, but it was wierd that the eras also did not produce any sound.

Remember that setup of all components went smooth. No problems at all, except for the sub falling out of the sonos app.

After some thought, I think it might be something with the arc ultra since all config done in the app was related to the arc ultra. In terms of audio codec, the tv is the same, the hdmi cable is the same, and no other changes done other then connecting the arc ultra to a switch with a cable. 
Since I now have a working solution, I will let the family enjoy the christmas movies with super sound and I will try to remove the cables in a few week to see if things work on Wifi only.