Welp... seems like the firmware doesn't work for Windows 8.1.
Worked well when I had Windows 7 though.
Error "C:\Users\User\Appdata\Local\Temp\nsi88A2.tmp\nss8932.tmp" cnep
"'C:\Program Files\FiiO X3 Driver\TUSBAudioCpl.exe' -hide" did not return within 30000ms.
Looks like I'll have to send in this error to FiiO >.>
I can confirm that it does work with Windows 8.1 64-bit. You have do boot with 'PC Settings, Update & Recovery, Advanced Setup, Restart Now' and disable driver signature check or something like that while booting to install the driver.