I've had the KS8000 for just over 6 months now and never any problem with black screens... the PS4 Pro HDMI cable worked day 1, the old PS4 cable worked for my Samsung K8500 blu ray player, no problems.
I have nothing between the TV and the HDMI connector. Is it possible you guys might be relaying everything through some other things along the way? Would they maybe have really, really old HDMI cables that you haven't switched out during all your switching out? Or have trouble with the signal? Some sound system, video capture or console switcher things?
You may not have anything of the sort, but it's just a thought, and I think I'd read people mention that when I was wondering if I should bother getting fancier cables for "better" picture.
How can this be? My ps4pro is connected directly to the one connect box. I have tried four different cables all with the black screen problem. Are you using the auto setting on your ps4 pro?