Xbox Series X & LG C9 OLED eARC Help

Hello everyone! I hope you're all doing well today. I've come to this forum as I'm having a bit of an audio issue with my current television and soundbar set-up, and figured I'd get some help from people much smarter than I. I've owned an Xbox Series X console
for over two weeks, and I love it! I have it hooked up to my 65-inch LG C9 OLED television, which only makes it better. Just this week, I purchased a new soundbar to replace the one I had - I bought a Samsung HW-900QT 7.1 Soundbar as it had eARC capabilities
and both Dolby Atmos and DTS:X support, which my previous soundbar did not have. And so far, even though my TV and soundbar are different brands, they seem to be cooperating pretty well. Dolby Atmos works fine on my Xbox Series X, but after trying a few different
sound outputs, I have run into two issues:

#1 - I cannot use DTS:X. When I try my Xbox says that my receiver does not support DTS:X, and goes back to Dolby Atmos

#2 - I tried out 7.1 uncompressed audio, and while playing Modern Warfare, I could hear most sounds, but could not hear the announcer or my character talking when selecting killstreaks. I tried several different audio options found in Modern Warfare, but
to no avail

What am I doing wrong here? To give you some more info about my set-up:

-The software/firmware on my LG C9, Samsung HW-900QT, and Xbox Series X are all up-to-date

-I have the DTS App downloaded onto my Xbox Series X, and under the DTS:X section it says "Good to go!", but under the home theater section the option to turn it on is greyed out

-I have both the ARC and eARC options turned on under the sound menu on my LG C9, and it says "eARC" on my soundbar. For digital sound out, I have it set to passthrough. I have "Auto" and "PCM" as two other options for digital sound out

-I am 99% sure I am using an HDMI 2.1 cable from my soundbar to my television - this is the cable I'm using - https://www.amazon.com/gp/product/B07S1CGQ9Z/ref=ppx_yo_dt_b_asin_title_o06_s00?ie=UTF8&psc=1

Any information will be appreciated, and I hope you all have a great day

:)