After much forum-exploration, I've found that many people have had either a similar problem as me and solved it, or the same exact one and not solved it:
For audio, I use HDMI out -> converter (to optic) -> receiver -> speakers. Just recently (for no obvious reason) my laptop stopped recognizing the HDMI cable plugged into it. All of my drivers are up to date, and if I unplug the HDMI cable, my laptop makes a sound letting me know that something's been unplugged. I've tested the receiver, multiple cables, the converter -everything- but no dice (it must be my computer, eh?). I've tried "Show Disabled Devices," checking the Device Manager, and every other solution that the internet has offered, but I don't know what's up. This is my Sound settings with the HDMI cable plugged in:
When the problem first occurred I was using Windows 8.1, and the general consensus I had received on upgrading to '10 was "If it ain't broke, don't fix it." Now something was awry, so I tried solving the issue by upgrading to 10. That didn't work, and I now have Windows 10 and the same exact issues. Anyone have any idea of what's going on here?