I had enabled media device usage, but I didn't have the second of those drivers installed. It seems to be able to connect just fine now. Whether or not my attempts to flash the new OS version will be successful is an entirely different matter.
EDIT: Thanks to you too, Lynk. I wasn't sure which of the dozens of support forums I came across to trust. Your recommendation means a lot though, so I'll bookmark XDA-Developers. Thanks mate.