I had just the opposite problem of having rather bass shy headphones. As ultra portable amp i use the headstage arrow 4g, it has both a two step bass and two step treble boost (3db and 6db). To my ears much better sounding but more expensive is the vorzüge amp duo i own, as a big plus you can order it with custom bass and treble boost, ordered my one with bass +6db and treble +4db. Both amps are pretty neutral sounding without bass/treble boost.
Edited by GermanGuy - 5/27/13 at 5:21pm