Sonos ARC optimal DD5.1 configuration

Do you mean you’ve read all this? Audio hardware and software configuration

passthrough should be ON. Channels depends on whether the Pi is connected directly to the Sonos (better - 7.1 is OK) or to your TV (probably need to set 2.0 and AC-3 transcode)

Update: I see the Arc doesn’t have HDMI in and the LG doesn’t do eARC. You do therefore need to set channels to 2.0 and engage ac-3 transcode.