or if you have a spare deck (aka
dibba) or music system, get a connector for using the lineout of your soundcard to the microphone/line-in of the deck (not the best way though... lot of harmonic distortions esp. if you use bad quality connectors)
Some new music systems (Sony/aiwa) have spdif as well as USB connectivity (gr8 quality).
btw, 100W RMS or PMPO?
If PMPO, dump them and get better speakers for your computer instead of all the hassle above