Symbilink is your RCA cables pretty much. I believe you get a box and specail RCA cables. I think Symbilink uses really strong signal strenght and other stuff to get the best sound quality out of your stuff.
Symbilink is a balanced DIN cable, designed to use a 16V balanced signal to drive the amplifier with. There are symbilink converters you can purchase, and you'll have to purchase the cables. It's basically just like firewire cable, but I think they use their own special DIN cable.