Thank you for the information Rombaglonic.

I'd suggest checking the software drivers for the FiiO USB DAC and see if there are any more recent firmware or driver updates. If not, try reinstalling the drivers (or any program that may have come with the DAC).

Additionally, I'd suggest disabling any other sound devices that your are not using. Right click the sound icon in the system tray and select 'Playback Devices.' Here, disable everything that you are not using.

We hope we can be of assistance in helping you enjoy the exciting world of Final Fantasy XIV!