The sigmatel soundcard is an onboard soundcard. It can be that its nice, but its not good enough for music production.
I would recommend to upgrade to atleast an Creative Audigy, or higher: X-Fi or M-Audio or Emu soundcard.
Also, those thrust boxes aren't that good. They provide nice sound (I've heard several of thrust) but they aren't natural. They lack certain frequencies.
If you want to know for sure, visit a store like BCC or any Hi-Fi store, where they allow you to test speakers.
I have a
Creative I-Trique 5600 and although it is about 2 to 3 years old now, I still love its sound. Very good and deep bass while having a very good high end. Ofcource, I had to do some tweaking on my soundcard EQ to get them nicer than it standard is possible, but there's always room for improvement.
It would probably be better to pick one of the newer types, as they probably have better quality than my I-Trique.
But I must confess. Speaking about speakers made me wondering what's out there, and I've decided to upgrade myself

Edit: I've ordered the Creative GigaWorks S750.
Since I've updated my soundcard to the X-Fi Elite Pro, I can now have 7.1 speakers.
Do note that these speakers are expensive. A cheaper version would be the Creative Inspire T7900 (note: its a 7.1 set). They cost about 90 euro.
I must add that I've been lucky by getting some unexpected money
