Well, it doesn't have the correct cables for connecting to the GTX780. I say that because it has the correct PCI-E 6-pin cable but the single 8-pin cable doesn't fit. And when I muscle it (the 8-pin connector) in there, the system won't turn on at all. All the YouTube videos I've watched of 780 installations have the installer plugging both cables in very easily and it looked as if those two cable were already zip-tied.
I'll give it a try again with the video card but the original HDMI issue still exists.