My headphones can handle a ton of bass, no problem. But, since iPods (and every other MP3 player) come with tiny, low-end amplifiers inside, many bass-boosting equalizer settings put to much into the amp, causing sound to clip. Therefore, I'm working on two solutions:
1)Build the CMoy external amplifier, so that I can use any EQ, turn the volume to like 5%, and amplify with a better external amp
2)I've requested on Apple's iPod feedback page that iTune EQ presets made by you can be used on iPods.
So, I use the flat setting.