If you want to banish the speakers message from the TV you may need to use a remote that’s programmed for a different make of TV, e.g. Sony or Samsung. You’d teach the Beam to recognise those IR codes instead.

Two small changes. 

Optical is a one way connection, not two way, so normal CEC command processes won’t work, so you’ll need to set up your remote for IR use, and program the Sonos to read that, in the controller itself.

Also, the maximum bandwidth available across optical is Dolby Digital, so you won’t get the more advanced Atmos content. But beyond that, exactly the same. 

Thanks for the reply.

What is meant by ‘normal CEC command processes’?

The only command I would be interested in is volume control of the Sonos audio and that seems to work anyway even though the legend ‘loudspeakers off’ appears on the screen when activating volume on the remote. I gather that this means that the TV speakers are off (which I have selected in the TV menu).

The two-way command communication between TV and soundbar that takes place over HDMI, alongside the audio/video data. https://en.wikipedia.org/wiki/Consumer_Electronics_Control 

Optical is a unidirectional audio data feed.

The TV is seeing the IR volume commands from the remote at the same time as the Beam. As noted, this can be fixed by programming a remote to control a different make of TV, then training the Beam with those codes instead.

Even though I have lost the CEC (Viera) capabilities by using the optical connection from the Beam to the Panasonic TV instead of HDMI (ARC) I can still control the volume of the Sonos system using the TV remote control.

Surely this goes against the principle of CEC. I'm not complaining, just curious.

When you use optical, there is no ‘principle of CEC’ involved. There’s no connection. The remote is connecting via IR to the Sonos device. 

I seem to be missing something here. If I had a working HDMI ARC port what would I be able to utilise that I can't when using the optical port?

In the term Audio Return Channel where and what is being returned?

CEC, which is required for HDMI-ARC would allow you to control the soundbar from the TV.  In other words, the remote tells the TV to raise/lower the volume, and the TV then commands the soundbar to raise/lower via CEC. 

I've connected the Beam to the TV optical port using the adaptor and I can still adjust the volume of the Beam with the TV remote. That's why I'm confused.

It could be that the optical is set to variable, so the volume of the output can be raised/lowered.   That can work, but the volume level in the Sonos app would not be accurate. 

Your remote sends infra-red, your Beam receives it. No confusion necessary.

Either of those two options are feasible. The thing that isn’t possible is that there is a signal going backwards from the Beam to the TV set via that optical connection. There is no ‘sender’ on the Beam’s side, or a ‘reader’ on the TV’s side. Optical is a one way transmission in this setup, from the TV set to the Beam, and only carries the codec transmission, not any CEC data. See here. 

Thank you for all your answers.

I thought I had control of the TV volume by using the Panasonic remote but I don't.

I can adjust the Sonos volume by using the Sonos One back speakers which are not too far away. In the meantime I will have to attempt reprogramming the Panasonic remote to control the volume as has been suggested. I'm not sure how this can be acheived but I'll give it my best shot.

Further to my previous question, I have tried reprogramming my Panasonic remote to adjust the volume of the Beam but this cannot be done. Why would this be when it's an IR remote control.

In the meantime I have discovered a Genie remote control on Amazon which states that it is designed to adjust the volume on a variety of Sonos products including Beam 1 and 2.

I cannot find any reviews or comments on this remote so I wonder if anyone has heard of it.

I hadn’t seen that one, and it’s yet to acquire any reviews. At £17 it’s a bit expensive but I guess it’s worth a try.