I am not driving the headphones off of the RCAs directly. I am using the line-out of the empeg into the line-in of my PC and using the PC's output to drive the headphones.

But as I said I have already ruled out the empeg as a factor, since the same thing happens when playing the track in WinAmp.

I know the soundcard is not distorting it because I can crank the soundcard output (and the individual soundcard sliders) down to whisper-quiet and it still happens.

And the full-size speakers driven off of the same soundcard output do not distort at all.

And one certain pair of headphones off of the same soundcard output do not distort at all.

And by the way, read the FAQ entry on driving your headphones directly off of the empeg's RCA's. I have tried this with my little headphones and it works fine. Just so happens that it induces the distortion as well, but as I said, the empeg is long since ruled out of the equation.

It's definitely the headphones themselves and not any other component of the system. My question remains: WHY?!?!

What is it about different pairs of headphones that this particular song's frequency combinations messes up?