I have shared the DV settings in that comment too.
But are they really playing at 4k. In my case the signal from Firestick is only sent at 1080p 60Hz when set to auto resolution.
will check and let you know.
You can check this by pressing the I+ icon on the TV remote.
ARC can do DD+ and even Atmos over DD+ just fine. The only things it can't do are 7.1 ch audio and high-res formats like True HD. SPDIF can only do upto 5.1 channel DD.