Today's Work: I got the cable, and as I predicted, I can't communicate with the device. We didn't get video either, so we're wondering whether there's another signal we need to send or maybe a pin we need to ground. I'll have to ask my manager whether he still wants me on this decidedly non-software issue or whether I should move to something else. There may be a few other ways we can approach the problem rather than just poking at the cable.
An nVidia update failed on my desktop, and after restoring from a backup, the old crackling problem is back, where the audio starts to crackle after a while and muting the sound fixes it temporarily. I don't remember how I fixed it before, but I may have to experiment with the driver updates I have and see whether installing one of those might work.