Can you list which speakers we're talking about specifically. I'm confused by the USB comment. If they receive power from the USB bus, I would also assume there is a way for them to receive sound via USB, thus eliminating the need for the line-in. A make and model number will allow us to look up the speakers and make better sense of your problem.
What is hip?
Gear: Digidesign 003R / Telos Zephyr XStream ISDN codec / JK Audio Broadcast Host digital phone hybrid
PC: HP 6005 Pro MT PC running Windows 7 Pro 64-bit w 3 GHz AMD Phenom II x3 B7, 4GB RAM
DAWs: Sound Forge 10 Pro, Vegas Pro 9, Adobe Audition 3.0, Pro Tools LE 8.04, Reaper x64.