The easiest thing to do is to buy a BeoPort, has everything you need. If you connect the speakers directly to the Mac, you need to but a "BeoLab 2 Adaptor". Since the source is not using PL, the BeoLab 2 needs a trigger, thats what the adaptor is for. You also need to get a Mini to RCA adaptor for this kit if I remember right.
Joe
Its not just a product, its a way of life...