Audio not right on Dell XPS 410. Harmon Kardon speakers sound out of phase!

I have a Dell XPS 410 with Harmon Kardon subwoofer/satellite speakers that I bought with it. Playing some music the other day, I noticed the sound was "off". (Running Win 7 Pro.) I opened the SOUND feature in the Control Panel and 'tested' the speakers. When I click on the LEFT SPEAKER, I get sound out of BOTH speakers at normal volume. When I click the right speaker, I get sound out of BOTH speakers, but the volume is REDUCED. The speakers only plug in one way! Right speaker plugs into the subwoofer with a brown cable and the Left plugs in with an orange cable. (The inputs on the subwoofer are even shaped differently, so you can't mess it up.) The cable OUT of the subwoofer splits into two - green and black. They are plugged into the back of the desktop into the green and black ports. I tried to "update" the drivers on the "High Definition Audio Device" and was told the drivers are up to date. I doubt that's it's a driver issue. So why are they messed up? They've probably been like this for years and I just noticed it. They sound "out of phase" like the old days when I reversed the +/- speaker wires on my old stereo. Any help would be appreciated.