Best of luck - I have tried a ton of different devices and configurations (including the combo dave posted here) and none of it has worked for me. I honestly am at a loss because all the pieces are there and it still just doesnt work (cant get a signal to the pi at 4k even with 2 different scalers).
Please be sure to share your results!
I think you should buy "Dream Screen" from a startup which claims to do 4K and HDR. Otherwise one could also buy a ~$300 device that someone mentioned in this forum.
Personally I am still sticking to the windows grabber plugin for Hyperion which works with 4K and HDR.