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#11
Bit of a cop out but maybe bite the bullet Newegg.com - ASUS XONAR_DG 5.1 Channels PCI Interface Xonar DG Sound Card
Its an excellent soundcard, I have the DS version works great on win 7 64 .
Although I hate to give in so would probably try all drivers i could find for soundmax ADI 198x sound chip .
Here is a driver for another dell machine Dell Optiplex 960 Analog Devices ADI 198x Integrated HD Audio A05 Driver for Windows Vista / Windows Vista64 Free Download - Softpedia
Its a Vista driver if the set up doesn't find a compatible device you could try extracting the files with something like winrar, then using device manager point it to the relevant .inf file and maybe force a driver! it would not be the first time I've used this method on older kit.