I think you’ll need to turn off the CEC on your TV in order to ‘break’ the knowledge that your TV system has speakers already. 
However, I’m not 100% sure the Apple TV respects the CEC controls, either. The ‘hub’ device is the TV, and should have control over both the source device (the Apple TV) and the client (the Sonos Beam). Your best bet is to actually do the test, there is no danger that I’m aware of. 

Although I’m confused as to why you’d bother to have the Beam connected to the TV, and not use it.

Thanks for the quick reply Airgetlam. My plan is to use the HomePods solely for Apple TV content and the Beam for my television channels and DVD/Blu Ray content. I was wondering if the Beam would output audio from Apple TV as normal via the television if the HomePods were connected. Thanks.

Seems odd to give up 3.0 to instead use 2.0. 

There might be a setting in the Apple TV to turn off CEC, I have honestly never thought of looking. Or, you could get one of those adapters from Amazon to put on the cable between your Apple TV and your TV that blocks CEC completely. 

Still seems dubious to me, but you do you. 

I’m not sure what you mean by “give up 3.0 to instead use 2.0”? I don’t intend to give up my Beam if that’s what you mean, it’s brilliant I love it. I haven’t got the HomePods yet, I might never get them. Thanks for the advice about CEC, all the best.

The Beam is a 3.0 system, meaning it has a right channel, a center channel, and a left channel set of speakers in the one enclosure. It receives a Dolby Digital signal from your TV which sends those three disparate channels to the Beam for it to play. You can choose to add a pair of Sonos speakers as surround speakers, and make it a 5.0 system, or add a Sub to make it 3.1, or both to make it 5.1.

The Apple solution you’ve suggested is two speakers set up as stereo. So you would only get a left and right channel, and just the stereo signal from them. All the same information is there, but it’s crammed into two channels, rather than three separate channels. 

Ah right thanks for that. But it’s my understanding that two HomePods are capable of Dolby Atmos and 7.1 surround sound etc when paired with Apple TV 4K. However the new HomePod Mini is only capable of stereo when used as a pair. For the moment, it’s Beam all the way. Anyway, thanks for your help mate and I wish you a happy and peaceful Christmas