[Garry74]

I don't think DVI handles high bitrate but you could try.  Display port to HDMI should but you would need an adapter if you don't have one.  KODI should not be switching the O/S HDR.  LavFilters/madVR do.  Yes, set madVR to BT.709 with passthrough.  SDR will look better.  BT.2020 HDR will take over when and if it's applied.  I'm guessing at some of this because I don't use DSP but the settings should apply.  This is why I suggest diagnosing from Explorer to eliminate KODI and just use the raw tools to establish the basics.

 Thanks for the reply.

I have a display port to HDMI adapter, so I'll try that once I have the video part working smoothly.

Not sure what I can do from the desktop (I assume that is what you mean by explorer?), other than change MadVR, the resolution, turn HDR off and set up the sound.  

If you get things working in MPC-HC or MPC-BE, then the settings should carry over to DSPlayer as long as it is launching fullscreen. Having HDR engage would be because you have the OS HDR switch in Windows enabled, or you are sending the wrong gamut to the display. Set calibration in madVR to BT.709 and hdr to passthrough to the display with send metadata checked. Under that scenario, I can't see how 1080p content would engage HDR in madVR. This would not likely be the fault of DSPlayer.

The dual-GPU set up you had before might have been what was confusing DSPlayer with your past issue. 

 Thanks for the advice. I'll give it a go.

If I can get HD audio working at the end of it all, that would be a bonus.