P.S: Just had a look at your madVR setup video. Some questions/suggestions:
1) Is there a specific reason why are you blocking LAV Video? It should work the way you configured it, but with an up-to-date LAV version it should also work.
2) You have automatic display mode switching enabled in MPC and disabled in madVR. It might be worth a try to do it the other way round, to give madVR more control. Maybe that could help with the 10bit issues you experienced?
3) You have activated the MPC option "show controls in fullscreen mode". Maybe disabling that could help with the 10bit issues you experienced?
4) If you display 4K on a 4K TV with a 4K display mode, the image upscaling/downscaling options shouldn't matter because up/downscaling isn't needed. But for 1080p Blu-Ray playback, I'd suggest to disable the "upscaling refinement" options, and instead use better algorithms for image up/downscaling, and maybe also for chroma upscaling. DXVA scaling algorithms usually have rather bad quality (but they're fast!). If your GPU can handle it, try NGU Sharp Medium or High quality for image upscaling and SSIM1D100 for image downscaling, and maybe something cheap like Cubic for chroma upscaling. That should give you much nicer 1080p playback quality. Of course upscaling will only be performed if you use a 4K display mode.
5) Error diffusion is nice, but very expensive. Using ordered dithering is much faster and looks almost the same. Maybe if you save performance there, you can use better image upscaling/downscaling algos?
For your interest, madshi has posted a screenshot comparison with the Passengers Blu-Ray vs UHD Blu-Ray here, showing differences between various scaling algorithms:
http://www.avsforum.com/forum/24-di...or-mini-shootout-thread-607.html#post54983374
Upscaling the 1080p Blu-Ray with NGU Sharp comes surprisingly close to the UHD Blu-Ray! Compared to that, Lanczos looks awful. And Lanczos is usually better than DXVA scaling!