i think it was a NVIDIA 8600GS with 512 MB dedicated video RAM that shipped with that - i dont know what lead to motherboard your talking about though. There may be a lead running from front to the motherboard (normaly yellow header) + yellow base with pins sticking up. Which is your front audio connector. (F Audio)
what is more likely is its a realtek setup and the ports have been switched via the realtek manager panel.
What happens when you plug the speaker lead into the green socket ? A realtek box should open up. If you selct 5.1 surround or a surround setup you suddenly find your coloured slots have all been swapped around to in out middle rear left rear right !!!