Older onboard sound totally stinks for gaming to begin with! One reason for the popularity of the Sound Blaster line of expansion type sound cards besides the EAX effects is simply the sound quality in gaming and multimedia over the years.
The sound there isn't a separate card but an onboard audio chip if you are plugging the speakers into the rear of the board and not a card in a pci slot. The Dell support site is always a trip while they still show an X-Fi as well as an Audigy 2 ZS as the two other options for sound as seen at
http://support.dell.com/support/topi...D&doclang=en#2