Of course they are a fun sounding headphone, they are amazing in vocals, instrumentals, soundtracks, and classical is ok with them.
Without enough current, you won't hear any satisfying bass kicks and the bass won't extend as you'd like them to. Meaning an amplifier is recommended.
When amplified, the a900x gives a nice punch to the bass. Compared to the K550's I tried which sub bass was more present, but I preferred the a900x's bass kicks for EDM.
The mids on the a900x are not only good for vocals, but they play synthesizers very well. (E.g. Punks by F.O.O.L).
The soundstaging on these headphones mix in well with the other genres of techno. (E.g. Murder by The Crystal Method)
It is true that sometimes I crave for more bass quantity sometimes out of the a900x, but the EQ boost in FiiO amplifiers are enough to make me smile.
Edited by Nec3 - 9/1/13 at 1:00pm