HDMI cable can make a difference of course. About the BNC, some said a studio quality cable should be sufficient, but I found that the system sounds better with an "audiophile" cable.I found the HDMI cables make a huge difference, I have not experimented with BNC but it sounds like I should. A year ago Alvin recommended
https://usashop.sommercable.com/en/Cable/BNC-Video-Cable/Wordclock-SC-Focusline-L-Highflex-FL59.html
https://usashop.sommercable.com/en/Cable/HiFi-Home/Multimediakabel-EXCELSIOR-BlueWater-EBH4.html
The HDMI cable was way better than the $ 500 cable I had but not as good as the Audioquest Thunder 4K I am using. Maby start with the Black Cat cables.
My Atmosphere X BNC has a ground connector, and at first I didn't pay much attention to this extra ground connector (doesn't make much sense to connect additional ground specifically out of BNC cable(s) since my system already has ground (power outlet). Plus, connecting this ground wire requires a separate free outlet (cannot be connected to the same strip or any power conditional strip).
Anyway, last week my curiosity got the best of me, and I tried this additional ground with a dedicated unfiltered power strip directly to the wall. I didn't expect to hear any difference but the music sounded a bit fuller details were slightly better. I tried removing / reconnecting the ground and was sure it wasn't my imagination. I really have no idea why this can make any difference, because ground is ground and that other outlet also shared the same main ground of the house.