[Aguiluz]

The sound quality is limited by your speakers and many many factors. If you have "White Van Speakers," [Wikipedia] your sound quality will suck. On the other end of the scale, buying the best speakers you can find is also unwise, since the sound quality would be limited anyway by your Sound Card. You should strike a balance within the two.

If you want pure sound, fine, get those speakers with optical in (Like the ones used in "The Slayer") and a sound card with optical out. This ensures interference wont set in the wires (wires act like antennas) since the optical line is nonconductive.

If you hear a low "bzzzzzzz" from your amplified speakers when unplugged from your PC, now that's a sample of interference, probably since the DC voltage has ripple in it.