This is the model and specification of my motherboard:
http://www.gigabyte.com.tw/Support/M...ame=GA-8SG800P

As you can imagine, I've downloaded the audio drivers specified on
this page, and have already tried them.

Regarding you suggestion about purchasing the PCI sound card - prior
to doing so, I'd still like to try and understand what this is all
about.

Any more ideas?