We know that LG 5k display can work with flashed titan ridge card, without camera or sound support. I did some experiment on finding an easy way to enable camera and sound. There is an interesting cable like this:
It can connect usb header of your card in to one of Mac Pro's external USB slot.
I did two experiments on this cable: 1) I tried to connect my wifi PCIe adapter to Mac Pro's external usb slot using this cable so that bluetooth may work. But it burned my wifi card. 2) I tried to connect titan ridge's usb header to Mac Pro's external usb slot so that camera and sound of my lg 5k display may work. But nothing happened.
So, no solution yet...