ONKYO 5.1 digital to Asus A7N8X deluxe

[notinNEWYORK]

I am building a computer w/ an Antec 1040B2 case and an Asus A7N8X deluxe motherboard. The speaker system is where I'm having a problem. I bought an ONKYO 5.1 digital theater surround sound speaker system because the motherboard documentation said it would support such a digital system. However I can't connect it properly. I looked at the digital cable that came with the speaker system and it won't connect to the audio ports in the rear panel. Now this motherboard has 6 pin SPDIF1 audio connector (w/ 1 pin missing) on the board but how can you connect the digital cable supplied by ONKYO to that? The digital cable won't go.
I would try to connect to the speaker system w/ the analog connection but I bought it for digital. Is there an adapter for the connection? I will give thanks in advance for a helpful hand in this matter. Thanks
NotinNYC