Computer to AVR to 4K Smart TV surround sound setup

I’m trying to find the perfect settings for watching downloaded movies in 7.1 format. I have an older computer, HP ENVY with GTX 1080 GPU, 32 Gig ram, runs 4K no problem. Just purchased DENON AVR S970H AVR, with brand new Samsung 4K TV.
To put it bluntly, there are so many settings on that AVR and the TV for settings, it gets confusing. I have Windows 10 set to surround 7.1, and HRD is on. VLC just upgraded to 3.0, but all I have set there for audio is ” always decode in Dolby surround”. Some movies sound pretty good, some don’t. My old Denon AVR S740H would tell me what my input signal was … DTS, Dolby, DTS-X, Dolby ATMOS, so could set the amp to that, but this brand new 970 just shows ” PCM ” as input signal all the time but it will show all the speakers as active speakers in input and the proper speakers are highlighted for actual output…I’m to the point now where I have a button that says “Direct”, “Pure Direct” and “Auto” … I just leave it on Auto. I was wondering if it would make sense to burn my downloaded 4K movies onto a flash drive, and just plug the flash drive into the back of the TV and let eARC send the proper sound signal down to the AVR? I even went out and bought top of the line, 8K HDMI cables to connect all 3 units, because the ” HDMI ” test built into the TV said my cables failed. I have read the AVR manual, I have read the TV manual many times…there’s just so many possible setups.