Have you tried bypassing the Arcana, just temporarily, and connecting the ATV direct to the Arc just to complete the remote setup via the Sonos App ‘Settings/System/tArc Room Name]”? Then when complete, just restore the Arcana back into the loop. Maybe that will sort it for you?

Thanks for the suggestion. I did try a direct AppleTV-to-Arc connection but didn’t have any luck. I also tried connecting the ARC to a TV in another room with eARC, and that didn’t work either, so I wonder if it’s a hardware issue. I have tried factory reset.

Did you mean you tried a direct AppleTV-to-Sonos Arc connection? That’s what I was thinking you perhaps need to try?

Sorry about that - AppleTV-to-Arc is indeed what I tried (corrected above comment)

Also whilst you are in the Arc ‘room’ settings in the App, perhaps try toggling ‘OFF/ON’ both the infrared ‘switch’ and ‘signal light’ to help confirm that the IR is actually working and showing a connection from the remote - you will see the Status LED brightening and dimming if it’s working.

Looking at the guides online it says this about the ATV remote …

Goto Settings > Remotes and Devices > Volume Control. Now choose TV via IR (if it’s available) and if your TV is capable to accepting the connection you should be able to link it to the Remote.

The other option is …

Go to Settings > Remotes and Devices > Home Theatre Control > Volume Control.

Select the Learn New Device. If you have the option Auto or TV via IR that means your TV does support HDMI-CEC so you can automatically set it up. If not, take your normal TV remote control and point it at the Apple TV.

Press and hold the Volume Up button until the on-screen progress bar is full. Do the same thing with the Volume Down button. Your Apple TV should recognise these Remote commands and program your Siri Remote accordingly.

If you still have no joy with the ATV remote, then you can use any other IR TV remote to use with the Sonos Arc, if you have one there you can perhaps test? It will at least show if the Arc IR receiver is working okay for you.

My thoughts are that your ATV remote is ‘likely’ communicating with the Apple TV via RF/Wireless and not infrared and in-turn the ATV box is communicating with your projector over HDMI-CEC - but ideally you need an infrared (remote) connection to control your projector or ATV and once you have that you can use it to then also control the Sonos Arc.

You will need to take the same IR remote and select to ‘learn new device’ in the ATV settings. I think once that works it will then work to setup/control the Arc volume too. 

Good news: I successfully completed the Sonos Arc TV setup. It finally worked when I turned the AppleTV remote control setting OFF (instead of to TV via IR)and restarted the Apple TV.

Thanks for all the help, Ken.

Ah that’s great news, glad you managed to sort it.