Well today I've had a rude reckoning with this subject...

I've mentioned that under debian I've had no issue after swapping an 15 year old (before "smart") Samsung 40" TV with a dumb 4k 43" modern thing. I don't need the 4k and send 1080 to it, but in setting it up I did test 4k on a amd 7750HD and a Sky 500(~7870) and it worked fine.

From one input this 4k has been on a virtual machine running XP with a Quadro K600, no 4k available from the setup, 1080 fine and the sound works but the new 4k has seriously crappy sound, maybe a reason it's 50lbs lighter. It does have an unused hdmi return though.

So, a game day to enjoy the old XP super box. I'd never checked it as hooked up to this new 4k, just move the cable from old to new, never tested for the last year or so. So I boot up the previously perfect setup and the picture sucks with the typical bloomy bright washed out wrong color gamut issue. Any adjustment on the 4k's menu involving the HDR setting or the hdmi mode (1.4 or 2.0) fixes the display to a correct format without washed out colors. Just cycle the choices,. not even changing works. But, it then drops the sound! XP simply drops what was list as 'AMD HDMI rear channel' ? XP claims it's there and working, just not in the sound panel any more. Before, I thought HDMI2.0 broke the sound and 1.4 worked as is the case with the Quadro. This Sky 500 Display port not so, it's poor image with sound, or perfect image without sound. Bummer. I guess that setup needs a sound card.