I have the M-Audio Q40 and I bought them on recommendation from here. The problem is I'm not very knowledgeable about amps or headphones and the E11 is the only one I've owned. The bass boost is great with the headphones and I wouldn't be happy if I bought something and the bass was shy of what the E11 puts out. The E12 looks amazing but as its been pointed out I think I would be disappointed with the amount of bass unfortunately. I've found I like a quite dark bassy sound and I don't like harsh treble. It's difficult for me to choose another product and I'd want something similar to the E11 with the same bass response and just improve the tightness/quality and have better battery life. I love the E11 but I know there is better amps but I just don't know the names of them.
I have owned the Q40 and own the E11 and Z02. For quality bass with a visceral punch, you can't do much better than Q40 paired with the E11.