I listen to a ton of EDM, Rap, R&B and the bass reproduction is on point. If you think there's not enough bass from the HE-400, get a new DAC or AMP. Or your music files are not up to par and are mastered like crap.
Bought a JDS Labs O2 Amplifier from enbayo here: http://www.head-fi.org/t/632661/jds-labs-o2-amp last month and I didn't like how it paired with my Hot Audio DAC Extasy. It's a nice amplifier and comes with AC Adapter and can run on the internal 9v batteries. Will ship out via USPS Priority. Thanks for looking.