Can I use ATV4 to cast TV audio (from cable) to Airplay2 speakers AND soundbar?

Can I use ATV4 to cast TV audio from cable provider (Telenet Belgium) to Airplay2 speakers?

On top I want to keep the sound from the connected soundbar from the TV.

TV is a 2 year old Panasonic EX series

Soundbar is Harman/Kardon Sabre35 (connected via optical out from TV)

Speakers: Harman Kardon Citation series with airplay2 (at the backside of living room)

So to be clear: we are using a decoder for the cable tv, connected via HDMI and want to use both the HK soundbar as the airplay 2 speakers for sound.

Will this work in both ways? E.g. use ATV for apple music/spotify to send to all speakers and vice versa use the TV sound to send to all speakers?

I can not find a clear answer on this anywhere. Thanks a lot!