if it is a hardware equalizer actually amplifying the power to the headphones, then yes at stupidly high levels your going to mess something up, but when i am sitting in front of a computer, i use software equalizers which have no such risk, when they clip its clipping digitally, i am sacrificing abit of the sound resolution through doing this but the balance i get from the sound is worth it, in fact i always used an EQ, when i start using a new pair of headphones i have to gradually change the settings over time as the headphones burn in so that i get the same sound all the time