well IMO the 535 is more of a quality vs quantity, it has quality bass, when i owned the 535 thought it was bass lite, but it will depend on your amp you are using, e11 isnt bad, but theres room for improvement. imo one of the best ways and cheapest ways to improve bass would to get either a C421 or C5 Amp. jds labs has really gotten the bass boost right, it doesnt sound synthetic, its imo a perfect bass boost, ive owned both the c421 and c5 and both amp's bass boost are best ive heard.
aside from that, really you are limited to a equalizer, but imo i never eq any headphones to me its too synthetic, have heard a eq bass boost app that sounds good imo.. thats just me though