That's hard for me to say.
I'm not really familiar with lower end sound cards.
I have an Audigy 2 ZS which runs for $75 and I use it for my Klipsch 5.1 Ultras which are slightly better sounding than the 2.1s (+3 channels aside, the sub is much better).
I've heard many people saying that the sound card is very important with these speakers.
I'm still using some $40 Altec Lansing 2.1s that are like 6 years old now. For 2.1s, it is foolish to spend more than $50.
If you play games or listen to CD audio or higher quality then I disagree. There's a big difference.
If you're talking about internet browsing and mp3s, I agree.