Normally you should only need the SPDIF connected to your receiver.
Doesn't your stereo receiver drive your standard speakers?
Or are your speakers the 'self powered' type? What kind of input options do the speakers have?http://www.newegg.com/Product/Product.aspx?Item=N82E16829132007
ASUS Xonar D1 7.1 PCI Sound Card ($70 a/r) has the S/PDIF TOS-Link optical output I think you might need.