Download the one that say's Windows 98gold/98se/me/2000/XP/2003.
I ain't expecting this to work but because the dxdiag showed you were using a driver that is not digitally signed you might as well give it a try. When a drive is digitally signed all that it means is that MS has tested the driver to be compatible it does not mean that it won't or is not working.
If this don't work and the system is otherwise stable/running good I would just get a sound card and install it, it does not have to be a expensive one. There seems to be a lot of sound problems lately on new builds using this onboard sound chip and the only way around it at least that I have found is to purchase a card.
Disable the onboard sound in bios before installing a sound card.