First time poster here! I've been extremely happy with my Sonos Arc, 2 One SLs for surrounds and Sub 3 as a whole. I've recently realized that I had my setup running incorrectly and was only getting stereo PCM forwarded through my speakers, so I started changing a few things to get the best sound I can. Here's a summary of my setup:

TV: LG CX (65") running latest firmware

Sonos arc connected to eArc port with HDMI 2.1 cable. Nintendo Switch, PS5, and Xfinity 4k cable box all connected to other TV HDMI ports with HDMI 2.1 cables.

Arc, 2 One SLs, and Sub 3 all running latest firmware, as are the connected devices.

TV settings: eArc is toggled on, audio is set to passthrough with all HDMI set to "bitstream."

When I change the Nintendo Switch to surround sound in its settings menu, there's no audio signal detected at all. Automatic doesn't work either. "Stereo" will pull a Stereo PCM signal only.

What's weird is that a few days ago, I left the "surround sound" setting on the switch toggled on, and the next day when I turned it on again from sleep mode, it was working! Spontaneously! I was getting Multichannel PCM 5.1 as shown on the Sonos app. Then last night, it stopped working again.

Xfinity cable box works fine and processes Dolby Digital 5.1 which is all it's meant to output. Internal TV apps are doing Atmos and surround sound as needed.

I've also noticed with the PS5 some finicky scenarios. I only get sound with the "7.1 channel" setting selected (Multichannel PCM 7.1). When I select "5.1" on the PS5 settings, audio signal is lost again. It works fine transmitting Dolby Digital 5.1, but I would prefer the lossless LPCM if possible.

I apologize for all the information. Just trying to get the best I can out of my system. It's turned into a bit of an obsession. I'm just not sure where the error in the chain could be occurring.

For reference, it appears I'm not the only with this setup that has struggled. 

Any tips would be greatly appreciated!