I'm not sure about the status on Windows 10, but the firmware you're asking about is a combined firmware and bootloader that can be flashed with a programmer (pickit, bus pirate, etc).
Thanks for the hint!
In the meantime, I set up a Windows 7 virtual machine and flashed the firmware with the windows version of the Diolan tool. I'd love to be able to flash using Linux, though. Has nobody else had problems? Is it maybe a distribution or kernel version specific issue? (Kernel 4.9 being "too new" for those old tools?)