Answered in the Simplix thread, either use the updatepack or use the driver manually, as described at the OP of this thread.
You go to the Mediafire link and press Download. There is no Login required here. The password is for opening and extracting the downloaded archive.
It worked ! ! ! Thanks so much! The Dell/Intel USB drivers for the Optiplex 7050 are a known conundrum, so it's a relief to have such a quick and easy solution. So I now have UEFI + Secure Boot. Accomplished via Win 10 bootloader and cheap graphics card supported by Win 8.1 drivers. I haven't tried UEFISeven, yet, because I still need to learn about key tools to allow a modified boot system to secure-boot in Dell's BIOS.