If you mean the ball-shaped Apple Pro speakers, the only non-custom way is with a discontinued Griffin Technologies adaptor that, due to demand and short supply, can sell for over US$200:
http://www.amazon.com/gp/offer-listing/B00013MRT8/ref=dp_olp_0?ie=UTF8&condition =all
Your current issue is that the audo ports on your MP do not provide power. The special audio port on the G4 Cube and other comtemporaries was special in that, in addition to providing an audio signal, it provided power to the speakers. Otherwise the speaker have no power source. Another technology that Apple created, hyped, and then let die.
Someone posted a link to instructions on how to home-build an adaptor that would work similarly to the Griffin iFire but I can't find the link at the moment. I recall that the build was not a trivial task.