Dolby 5.1 Not working via Apple TV 4k

Noticed that my Apple TV 4k is only sending PCM Stereo signal to my TV which is conncected to a Sonos Playbar via optical, using a couple of Play 3's as surrounds along with the SUB Gen3.

Every other device including the Apple TV app on an Amazon Fire Stick 4k is fine.

Messed around with the audio settings on both ATV and my LG 4k TV - nada.

Also have seen this as an issue for others, wondering if there's been an fix posted anywhere?

Seriously disappointed!

I use my ATV box for almost all of my streaming, have spent a small fortune on TV Shows and Movies on iTunes and prefer the quality of the picture on the ATV to any other source.

Would appreciate any help on getting this sorted.

All devices up to date for firmware/software.