Update. If I boot with HDMI, unplug and plug in DP, it works. If I boot with DP, I have to unplug DP and plug in HDMI and then it works. In both cases, the sound icon flashes and sound occasionally skips. I wonder if installing 10.13.6 over my current installation will fix the AppleHDA kext and work. I figured as much with DCPI manager by nature of what it does. I'm comfortable installing it, just wanted to make sure. I just cloned my drive, so I'll give it a shot. Thanks again for the great work.