If you like neutral sounding headphones, why are you boosting the bass and using equalizer settings like rock? That's counter-productive. I woud find a frequency repsonse graph for the S4 and use the equalizer to try and even out the frequency responses, or just to lower the treble if you feel its too bright. Going to cheaper headphones probably won't help, because cheap headphones are not usually accurate. I would check out some headphones that are used for monitoring if you want something neutral sounding. Are you sure you have a good fit with the S4's? You could be turning up the volume to compensate for not having a complete seal.