I used to think sound cards were just a big marketing scam, that is until I bought a sound card for my old computer.
A cheap $30 C-Media CMI8737, The sound quality blew me away...
so i picked up another one and put it into my gaming system.. they never sounded so crisp...
And this is a cheap $30 card!!
Go for it, an X-Fi or Audigy2 will rape you're onboard alive.