My onboard sound was pooping out on me, so I put in a old Soundblaster Live cheapy that I picked up for 30 bucks at walmart, and the sound is a lot better, not super great, but better, and clearer. But of course, my onboard audio was messing up in the first place. My speakers are also Creative brand 5.1 set up, the cheapies as well.
I have said this before, that I save the high end audio for my theater, onboard and cheap cards are good enough for my computer purposes. Although I would go all out for a graphics card, but that's a different story altogether.