I was in the same boat as you with my P65-F1 and older Vizio sound bar with my HTPC. I was trying to get 5.1 audio in games but also wanted to keep 4k/60hz and 1080/120hz video output.
Unfortunately with your current setup you have to choose one or the other since Windows outputs 5.1 (or 7.1) LPCM uncompressed audio in the vast majority of games and the Vizio TV can only pass through 2-channel PCM from the HDMI-ARC port.
If you go the other way and pass through the sound bar, Windows should detect that you have 5.1 surround BUT won't allow more than 1080p/60hz and 4K/30hz video because the soundbar only has an HDMI 1.4 port.
To get around this you have a few options:
1 - Use a modded audio driver that allows Windows to output in Dolby Digital 5.1 (called Dolby Live) audio instead of LPCM. Try this video and the links under it.
https://www.youtube.com/watch?v=zd3XZWt-KQw
I did this before eventually upgrading to an Atmos soundbar setup and it worked for nearly everything with a few hiccups here and there.
There are a few different files you need to install to get this working but it's not too hard to get set up.
2 - Create a "fake" second display in video settings and output only video to it (there is a setting for this in the Nvidia control panel under "setup digital audio"). Put the resolution on the second display to something really low to reduce overhead. Run one HDMI cable to your TV for video and the second cable to the soundbar to carry the audio. This can be wonky but should allow windows to detect and output surround audio. It MIGHT limit what can be output on the video only output but you just have to try it out to see. Obviously this requires 2 HDMI cables to run from the PC. Depending on your card, you might need a displayport to HDMI adapter.
3 - Upgrade your soundbar: Newer soundbars will have HDMI 2.0 (or 2.1) ports and will allow 4k/60hz and higher video passthrough along with HDR while supporting all surround sound formats from Dolby Digital, Atmos, DTS and full LPCM.
Connect the HDMI from your PC to the soundbar and then from soundbar to the TV and everything should work the way you want. Obviously this costs money but hey, it's the easiest solution and it's what I ultimately did.