KDE4
Left click on the Mixer icon on your taskbar, like this and if you have more than one audio device, choose Audigy:
Digital Output button is not normally shown, so navigate to Settings / Configure Channels.
Scroll down until you find
Audigy Analog/Digital Output Jack:
The button will now appear in the mixer and you can use it to toggle / enable the SPDIF / Digital/Analog output:
Have a lot of fun.