Yes- using alsamixer you should see a control that is called IEC958. It is a "switch", cursor across to it, press M to switch it on and off. Turn all other volume controls to full. If below the slider there is an "M" the channel is muted, so unmute all channels.
As you change the IEC958 switch from Muted to On, you can actually see the laser switch on and off. Do *NOT* stare into the digital optical output from the motherboard to check. You can just put some paper over the laser output socket (SPDIF socket), or even your finger.