Digital Audio over multiple speakers from TV

I use Google Home to play music via my Naim Uniti Atom Headphone Amp to my loungeroom speakers (Adam Tensor Deltas) and my Kitchen Speaker (Naim Musso V2).
With Tidal, Soundcloud etc etc i just click the 4 small dots in the bottom right hand corner of the app so i can activate the 2nd speakers and the music will sync and play on both.
When im listening to youtube via my tv - which is connected via TV digital out and into the Digital in (3) of the Naim Uniti Atom i can play via multiple speakers?
It lets me select the 2nd speaker and visually “activates” but no volume comes through the 2nd speaker?
Any ideas?
I have PCM selected as a sound setting on my TV.
In summary i am wanting to play youtube music via my tv over multiple speakers
My TV is a Samsung Frame

I do not have a HDMI ARC option on my Uniti Atom HE. Only digital.

Apologies - I hdo not ave PCM selected as a sound setting on my TV.

Profile not up to date?

Uniti allows digital inputs to use multiroom. Ensure input is active in app and correct input is used.
Check optic cable and signal from tv, and that all settings in tv are correct.

If lip-sync is vital, you will notice a lip-sync issue when using multi-room.

Thanks guys.
Lip sync is not vital.

Im starting to think its the tv…

To recap, are you saying there is sound from Atom speakers, but despite selecting Muso in multiroom, you get no sound from the latter?
I suggest that when you have the opportunity. You switch off absolutely everything - not standby but mains off. Restart the router, and after a short(ish) period, switch on Atom and Muso, then control point. Leave tv unplugged at this point. Whatever control you use, switch off bluetooth and close all apps and then turn the control point off when you do the router. Any other phones or IoT items - all completely off.
Try first, iRadio - choose a reliable feed like RP (see Naim’s choice) and get multiroom working.
When that is ok, then leave it playing and turn on tv - select whatever has not worked previously and then just change the source on control point - multiroom will remain selected.
One option if you think it is the tv, is to do a factory reset - caution - you will loose any apps you have added potentially.
Remember the switch off everything and see how you get on.