Disconnect everything from the TV including the Arc and unplug the TV and Arc from power for a couple of minutes. Plug the TV and Arc back in but keep the Arc disconnected. Be sure Anynet+ (CEC) is enabled in your TV settings, then run TV Setup in the Sonos app. Follow the instructions in the app and connect the Arc to the TV’s HDMI ARC port when the app instructs you to using the Sonos-supplied HDMI cable. When the Arc has been successfully connected, connect any other external device to your TV.
Worked perfectly. Thanks!
I was unable to solve my very similar problem with the solution above. I have a Samsung 5500 HDMI-ARC (not eARC) TV (purchased in 2017) and just bought a Beam from Costco. I’ve tried everything listed above to get the settings to “stick” but each time the TV is powered off, it reverts to the internal speaker. Going to the Samsung’s settings, the “reverse” option isn’t even on the menu. It only appears if you power the Sonos beam off and then turn it on. At that point, the Samsung recognizes it and uses the Sonos beam without any action on my part. I even tried connecting the Sonos as a “remote speaker” but the Samsung menu told me that it could not adjust the volume with the Samsung’s remote and to use the remote that came with the remote speaker. Neither of these methods is acceptable. The firmware in the Samsung TV is up to date. Any/all suggestions are greatly appreciated.