Onboard sound is too finicky to give anyone any assurance it will work. I've seen the smallest change kill the onboard sound. The only cure I use that gets the machine out of the rut is another sound card. My three choices are...

1. Any non-Aureal based PCI sound card (runs about 10 bucks.)
2. A Turtle Beach sound card (sidesteps Via/other chipset issues.)
3. A SB Audigy card.

Bob