To get madVR to passthrough HDR data successfully on Windows 10 1703 I did the following:
Update to madVR 0.91.9, LAV filters to 0.69.0.43, NVIDIA drivers to 381.89
NVIDIA Control Panel settings:
http://i.imgur.com/M5KxTx3.png
Windows 10 System settings:
http://i.imgur.com/23Mp535.png
Player Properties:
http://i.imgur.com/CMDgYy2.png
madVR settings:
http://i.imgur.com/qoR6NV6.png
http://i.imgur.com/XpRAzbx.png
http://i.imgur.com/4Pl6Rk1.png
Picture quality looks exactly the same as when using the TV's internal player.
Also, both NVIDIA's private API and Windows 10 API produced the same results but I only tested with one video file.
I used DDU to do a clean install of the display drivers.
Windows 10 1703 was a clean install not an update from 1607.