What is powering your headphones? Are you using 1/4-inch or 1/8 inch cord for headphones? (I don't know if that makes a difference, but I've never used 1/4 inch so that could be your problem).
Whatever output your computer has you should plug directly to your stereo (I'm guessing you have one with an aux input) and then use the stereo to amp the headphones. That shouldn't be a problem.