Ok from what I gather that purple motherbd connector should match up to the black logitech connector. Logitechs installation guide doesn't give what the colors are for "Just match up the colors to the same color on the rear of the computer"
btw on your pc:
Blue = Line in
Lime = Front L & R
Pink = Mic
Yellow = */PDIF (optical connection)
Purple = Rear (Surround) L & R
Orange = Center & Subwoofer
Yo may need to go into the Nforce control panel and set the audio to 5.1 if you had previously set it to 2 spkr. The user manual says it should autodetect it though.
edit - You will need to set the subwoofer to 5.1 also, the switch appears to be on the back of the sub.
98 SSEi 111,222 miles.
Intense PCM, LS6 Valve springs, PEMS, FWI. Hawk Street Pads.