Mhhh... this enforces the possibility that you were just clipping the HPs... Could you try at a much lower listening level?
Unless, of course, either HPs or the HPs Output are broken... :o
well, i've used the bose headphones with regular music and they sound great, I tried at levels barely able to hear to decently loud and the tonality was the same on the distortion tones. the clean tones were decent, passable at least - i could tell the difference between a 2 rock and a reinheart at least but I don't think they sounded as good as they do through the cab