Gigaworks S750

Guys, what happen if I combined Creative "Gigaworks S750 (7.1)" analog speakers with custom speakersc? le me more explain.... first I connect the S750's Subwoofer only with my sound card, then I connect (by RCA) the 7 different custom made High-Fi speakers into the S750's sub rather then S750's...

Hi I have built a HTPC and am using the Asus Xonar HDAV 1.3 Slim soundcard I have my original Creative Gigaworks S750 7.1 channel speakers. These do not have any optical or spdif input How do I get the spdif out of the Asus Xonar HDAV 1.3 Slim sound card to connect to my creative 7.1...