sound question

Just one simple question:

I have a SoundBlaster Audigy, it's got analog and digital outputs.  I 
know that both work, I had them both working in the same layout with 
Linux.  I just want to know if the fact that I can't get any sound out 
of the digital outputs is

a) because the driver doesn't know about the digital output, or
b) because I have it misconfigured
c) because I'm doing something horribly stupid.

I'm willing to do more investigation, but I want to start off in the 
correct direction, so a word to start me off the way would help out.

BTW, I have a amd64 on this machine, but I could also try the i386 machine.