[drpizznock]

Why did you do that? Is there some problem with newer drivers?

I'll get into disabling HDR for Windows 10, I'm assuming it's fairly easy to do?

I'm familiar with Kodi DSPlayer with MadVR, although using it before didn't show any difference compared to Kodi 17.6. Aside from turning off Windows 10 HDR, is there anything else important I should configure in Kodi DSPlayer? 

They were the last drivers that worked flawlessly for me. I keep HDR disabled in Windows 10 since 99% of my content is 1080p or lower res 8bit. 

Before your TV will properly display 4K HDR10 content HDMI UHD Color needs to be enabled in the TV's settings and MadVR needs to be configured to pass HDR metadata through to the display. Check that thread for info on how to configure audio which will also be important.