Not so much a question as an observation. I recently bought a new Atom, very impressed with the sound quality. This was to replace a Sonos Amp in the second lounge/playroom/music room in our house (we have a longer standing SN2 and ND5xS2 in the living room). However, to be a good fit for the room the Atom would need to play nicely with the Sony Bravia TV in the room - existing control was via braviasync (which is just a brand name for HDMI-CEC). Straight out of the box I was having issues whereby turning off the TV wouldn’t turn off the Atom and the signal would drop on tv standby meaning the Atom wouldn’t play HDMI if the TV was cycled to standby and on again. I checked the settings, turned everything off, reconnected and the problems persisted. I was on the verge of returning the atom.
However, before going down that road, I read something somewhere about ground loops on aerial connections affecting HDMI behaviour so disconnected the aerial to the TV but it made no difference. Read another post on another forum which indicated the quality of HDMI cables could impact HDMI-CEC behaviour from sound systems and TVs. Bit the bullet and ordered some higher spec HDMI cables for the Atom and the Apple TV (not going to mention brands, but the 8k compatible cables apparently have less susceptibility to interference). The class of new cables I purchased were Ultra High-Speed HDMI Cables.
Swapped out the hdmi cables on the Apple TV and Atom. Noticed the hdmi cable on the Apple TV wasn’t quite cheap and nasty but was a bit old (at best it was a High-Speed HDMI Cable ) - I suspect it was causing the problems I experienced. Since then the problems have disappeared and HDMI-CEC works as expected across the TV, Apple TV and a Chromecast which is also attached.
So the moral of the story is to check and swap cables if you experience similar issues/behaviour.