You're right the 815 chipset family has like 5 different downloads, but they might just be the same.
http://downloadcenter.intel.com/filt...s=19&submit=Go!
has a few of the relevant downloads. If you're really unsure, download the chipset identification utility. It could help you identify the components you can't find drivers for.
It could also be that although the ethernet and audio are integrated on the motherboard, that the motherboard was made for an OEM, and only they would have the drivers to the third-party sound and network drivers. If you know the make and brand of the PC, you could try looking on the manufacturer's web site.
Otherwise, try the unknown device identifier:
http://www.zhangduo.com/udi.html