Whats wrong with the Tanix TX7 S905X box. Cheap and highly specced and supports UHD and gives HDR too though I only have a FHD TV with an excelletn picture quality right now as unable to afford to change TVs. I used the Beelink MXIII II S905X box before and that was even better but no longer available.
I'm also a fan of the Tanix boxes, the TX7 is probably the best one they made.