Yes you will, though I would steer away from the Audigy line; been obsolete for about 6 or 7 years now.
Low end, the ASUS Xonar DGX, for around $30 or so, is a step up from onboard. Moving up to about $70, the ASUS Xonar DX, while a good 6 years old now, still reigns supreme. At $99, you have the Creative Sound Blaster Z. Above that, its really hard to justify getting a soundcard unless you have a REALLY high end set of headphones that need an amp to drive; that's where the ASUS Xonar Essence ST(X), ASUS Xonar Phoebus, and Creative Soundblaster ZxR start showing off.