Why USB Only? That's a question we'd like to ask Altec Lansing after we saw these 5.1 Surround Speakers. The FX5051 has an auxiliary port and headphone jacks, but they're stereo-only, which would negate the point of buying a 5.1 system.
The whole system costs $249.95, and relies on you to have at least Windows 98 SE to take advantage of the USB connection. We're not sure about Mac support, but it does come with a remote, which is actually pretty useful so you don't have to reach or crawl to fiddle with the volume.