I never had any decent luck with onboard sound cards, though most of the times my motherboards were nothing to brag about. I have a Soundblaster X-Fi Xtreme Gamer Fatality, which I got for $50 bucks off, and love the dang thing. Sure the x-ram may be useless in all but a few games, but the sound from it, especially with my plantronics headset (yes I am somewhat ballin for being a college student whos married, has a kid, and another on the way). It's just awesome. My opinion, get a pci card. Take that small insignifigant burden off the processor, and enjoy better sound.
