Just last month I upgraded my old 5.1 Altec Lansing that I've had for 5+ years to the Klipsh Promedia 2.1
Initially I figured I could get a cheap $50 speaker system and be satisfied with it, but after checking the demo units at Target, Walmart, Fry's and Best Buy, the Klipsch sound was dramatically better than any other 2.1 displays. The sound (IMO) was even better than the Bose speakers that retailed for twice their price. I really couldn't force myself to buy the $50 speakers after hearing these guys.
I'm only feeding onboard audio to them, but the sound quality is spectacular, I'm not sure if upgrading the sound card would have a noticeable improvement in audio quality, but thats what I initially thought about $50 speakers too.