Unless you upgrade your speakers to a 5.1 or 7.1 (!) setup, I dont think it will make *any* noticeable (audible) difference. I was using my integrated sound chip (SoundMAX on Asus P4C800Deluxe) and yesterday I started having some problems, and so I bought a Soundblaster Live! 24-bit (for $29.99 at CC) and noticed no differences whatsover (except it is stable and doesnt cut off like the motherboard sound chip - but that's a story for another day/thread).
I have the same speaker setup as you as well (2 satellites & a sub under my desk). I find it adequate for my gaming needs. BTW, I do not watch video/dvd on my computer.