Not to rain on anadtech's parade, but there is a great forum to discuss soyo and other AMD motherboards:
http://www.amdmb.com/vb/forumdisplay.php?forumid=25
Basically, the expansion board enables you to hook up your PC to a 5.1 receiver to get surround sound. The optical/coaxial outs are meant to send digital sound output to an external decoder such as a receiver. The inputs are to pass a digital signal into the PC for capture/editing purposes.
From memory:
Install dragon plus
put expansion card into a free PCI bay (1 or two is best for airflow, also 1&2 seem to be less stable than 3, 5 and 4 in that order)
plug it into the proper header on the mobo (RTFM

)
get the new CMedia drivers, install them
double click the C-media mixer that appears in the taskbar and select "use SPDIF passthrough".
Try the amdmb.com forums, they are really great, particularly for soyo mobos.