if its the dell control board (I've got the dell) it predates the faster DP standards. It only supports 5k via dual link. Which is why a couple years ago when the newer 5k displays came out, I snapped up mine from some guy on ebay upgrading and selling it at fire sale prices (nothing like new hardware to lower the value of perfectly good old stuff).
This is correct! Though there is a newer driver board which supports USB-C (and thus one cable), but it's a lot more expensive. And since I was connecting to an 2015 iMac, wasn't needed in my case.
