MBP 2018 4K 60Hz 4:4:4 8-bit color (instead of 4:2:0 10-bit and broken HDCP)

Have been using a MBP nTB 2016 with my (a) Belkin USB-C to HDMI converter, (b) a 2018 Denon receiver, and (c) a 2015 Samsung TV. This combination gives me an absolutely wonderful display of 4K 60Hz with 4:4:4 chroma and 8-bit colors, basically the best one can do with my setup.

Bought a new 2018 MBP, and with exactly the same setup, I get a garbled display that is all green and purple. It also breaks HDCP in a major way (iTunes worked fine before, but now throws the "The fIlm will only play on displays that support HDCP" even on the internal retina display, with no external displays connected).

Did some investigating, and my receiver tells me that my new 2018 MBP is outputting 4K 60Hz but with 4:2:0 chroma and 10-bit colors. I suspect the problem is that my TV cannot handle 10-bit colors.

So, my question - how can I force the 2018 MBP to output 4:4:4 with 8-bit colors? This is something that even the 2016 MBP could do.

I can turn off "UHD Colors" on my Samsung TV and / or "Enhanced 4K format" on my Denon receiver. Doing either is enough to make the 2018 MBP stick to HDMI 1.4's 4K 60 Hz with 4:2:0 chroma and 8-bit colors. But the subsampled chroma is really not ideal.

PS. any ideas to fix the HDCP issue would also be greatly appreciated.

I have tried resetting PRAM, SMC, a complete reinstallation, and the HDCP error persists. My iTunes movies play fine on other computers, so this does not seem to be an account or software problem. Will go to an Apple Store to get the computer replaced if I can't get this resolved ....