I'm confused by what you're doing. I'm sitting here with a pair of Skullcandy MIXR headphones sitting on a table in front of me. I have my iPod plugged into an amp. I am cranking bass-heavy music loud enough for them to be equally loud as my laptop speaker - there is no chance they are going to sit on my head with these volumes. Yet I'm not hearing any distortion.
What source and amp are you using?