OK good. then checked spec sheet, LG SK9Y got:
1x optical in
1x 3.5mm in
1x HDMI in (4K HDR pass through)
1x ARC HDMI out (4K HDR pass through)
So will my setup like this correct?
1) PS4 pro HDMI out connect to TV HDMI in + optical out connect to LG SK9Y optical in
2) TV box HDMI out connect to LG SK9Y HDMI in
3) LG SK9Y ARC HDMI out connect to TV ARC HDMI in
This ensure my PS4 pro can play 4K HDR direct to TV but audio will be using optical since PS4 pro dont have dobly atmost (unlike xbox one S).
Then I will be able to play 4K HDR video content from TV box with 4K HDR pass through LG SK9Y to TV.
Then with ARC HDMI between LG SK9Y and TV, occasionally I can play movie/audio direct from TV to LG SK9Y without TV box (though this may not work as per read in this thread).
Correct?

Why not PS4 to SK9Y then TV. Just simple with two HDMI cables connection since SK9Y can do 4K HDR pass through from PS4 to TV.
Like what jhleo1 said, PS4 -->SK9Y. You can play your blu ray movie with Dolby Atmos. Setup as below link