These beasties arrived in the mail today (hurrah!), but i'm a bit confused as to how to set them up. The cable in the box is the normal audio cable i'm used to (3 wires, green/yellow/black), but i've only got the one port in the back of the (intel) iMac. On the website they said the speaker system was digital, so i assumed that meant it would come with a single digital cable that plugs in the back (this came with some creative speakers i got a few years back), alas, the box has no such thing. Is there a really simple way to do this that i'm missing, or do i need to wander off and find a cable? If so, what?