I'd check the wiring siagram and specs on the usb device, but it looks like the 5.1 outputs are to be connected to that DIN-type jack on the left side of the pictures you posted.
Looks like a pain, when so many sound cards simply have 3.5mm output jacks on them for front, rear, sub, etc, etc...
Creative does have laptop expansion sound cards.
Try
http://creative.com