Since the power book only has one mini out put jack then what you can do is pick up a mini jack splitter for about 4 dollars at radio shack. now this will only work if your speakers has two mini jack plugs, on for the front set and one for the rear set. Now this won't be tru suroubnd sound, beacuse you are only using two chanel outout, the right front will be playing the same as the right rear. I hope this helped.
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I Have a Super Computer