Audio Problems

Excalibur 184 system. So I've had these speakers for quite awhile now and on the back of the receiver unit I've just been using the auxiliary cable on the back and have had to set it to only use stereo and not 5.1. I don't know what the cable on the back of the unit is called that will connect it to the computer using 5.1. The manual for the speakers is here . On page 5 of the manual it shows three cables that combine into one cable which plugs into the back of the receive of the speakers, if anyone knows what that cable is called or has any other ideas it would be much appreciated.

After doing some research I have stumbled upon the Mini-DIN connector cable. Is this the cable that is being used in this system? And if so where can I find a Mini-Din cable that converts to those three inputs?