You should be able to set 4K / 444 / 10bit only
for and under 30Hz. Tho' I have read elsewhere, that some TV's and more likely projectors can't accept 444 even on these lower Hz setting with 4K.
Personally I won't advise to set anything less than 50-60Hz for the GUI, and also because it seams that the HiMedia player would do an auto switch to 422 or 420 when a video is played anyway, even if you would set 444 / 30Hz for the GUI, which I don't know the reason why (maybe this is a compatibility fallback).
The best would of course it even with 4K / 60Hz / 420 GUI setting it would switch to 444 for any video under 30fps if the display supports it.
Tip: Check if the Box is connected to the right HDMI port on your TV dedicated to Bu-ray/Media Players and also set the HDMI source respectively in the TV's menu. And check if it's not in some kind of "limited" or "boosted" color mode both in the AVR and in the TV.