Did a little troubleshooting with Aviat0r on the Discord earlier. I fully disabled my antivirus and firewall (also added exclusions as recommended), re-extracted everything to a new directory, and started over fresh. No change.
I actually updated my video card driver at one point during the troubleshooting process, which uninstalled it entirely, but that also made no change.
Aaaand setting dxdisable to 6 seems to have done it! I'm at a login screen!
Thanks, everyone, for your help! I appear to be fully in the game now, and everything seems to be functioning as intended!