I looked at the speakers at polkaudio.com. Their smallest speakers like the R15 require 20W minimum to drive the speakers. All of their speakers are unamplified unlike typical speakers designed for computers (like Logitech, etc). To use home theatre type speakers, you'll need to run your sound card's line out to an amplifier like a home theatre receiver and connect the speakers to the receiver. A sound card simply does not have the amount of power available from the computer bus to power speakers like this.
Again if you would post the speaker and sound card models, a more definitive answer may be received.
Update: I dug a little and found some AMR series powered computer computers on Polk's site. These should plug directly into sound card with no issues. If you have these, perhaps you got a lemon. Test with another audio source as suggested above.
If you can plug headphones directly into the sound card with no problems, all of the software and drivers on the computer is working properly.
Gold/orange/yellow is usually subwoofer or game port. See
PC System Design Guide - Wikipedia, the free encyclopedia for standard colors.