Neither of those outputs go to the speakers. They are meant to plug into an amplifier that's capable of converting a digital signal to an analog one to be able to power the speakers via amplification. Now it's possible there may be one or two esoteric computer speakers on the market that have both a SPDIF input AND an amplifier with a digital to analog converter built in but they'd be pretty expensive if they did exist.

Those are both SPDIF outputs.. just different jacks that do the same job. One is for a standard rca cable and the other is for a fiber optic cable.

http://www.hardwaresecrets.com/every...-connection/5/