You’re presumably using Line-In Autoplay. Playback starts when it detects a signal and stops when it thinks the input’s gone silent.
There’s no way round this other than manually starting Line-In from the controller, instead of leaving it to Autoplay. Note that Line-In would then need to be stopped manually as well, otherwise the Fives would never go into standby.
The Five was not designed for TV usage. Line-In has a delay that’s too much for most people, upsetting lip-sync.
Sonos makes other speakers for TV, such as the Ray soundbar.
Thank you for your reply. Finally someone that makes sense. I’ll give it a try.