Well ZO Personal Subwoofer amp can get nice bass out of any headphone, it's been used to make even the basshy AD700 into slightly bassheavy! It's not only a gimmick bass boost device though, it performs very well for the price, many people who have bought it would have paid twice as much, that much of a satisfaction it brings, it's not your typical amp, it uses a slightly different implementation, it brings the whole frequency range more forward and which improves the dynamic range, also the soundstage size is increased a little and it allows 31 different levels of bass boost (I'd guess at the max setting we're talking about 13 ~ 15dB increase depending on headphone which is about the amount a super bassy headphone like Sony XB500 packs
)
For more info you can read my review
http://www.head-fi.org/forum/thread/558850/digizoid-zo-personal-subwoofer-review-the-missing-link-to-audio-nirvana
Or check out this thread for the overhelming positive feedback
http://www.head-fi.org/forum/thread/504037/mini-review-digizoid-zo-portable-subwoofer
A "v2" with further improvements is targeted for a September release.