4K Streaming and subtitle settings - DS218+ - Q90R - Apple TV 4K

Hi,

First of all my setup:

NAS: DS218+ , latest DSM, DS Video Server

TV: Samsung Q90R, Tizen, DS Video App, Plex App

Multimedia Streamer: Apple TV 4K, DS Video App, Plex App

AVR: Denon X3500H

Question:

I want to play 4K video from my NAS and I found out that my TV DS Video App performs the best with this task.

It plays various formats without any stuttering and flickering.

For some kind of a reason ATV4K has problems with the 4K HDR and frame rate when playing 4K video through AVR. Something to do with not being able to match the frame rate. I have enabled the dynamic area and frame rate match from ATV but still I can see a short stop in the playback.

I would like to use my ATV for playing the 4K video but Q90R performs better.

So, Is there a way to change my settings so I could watch 4K video from my ATV?

Secondly, how can I change the size of subtitles when using DS Video. DS Video App on my TV has only Medium and Large options and they are huge. Can I change them to smaller size?

TIA