I'm due for an upgrade and I am interested in purchasing a $300-$500 range pair of circumaural headphones. I want to purchase a portable amp to drive them for a few reasons: (a) I will be listening both at home and at work on a daily basis and (b) I have a pair of Etymotic ER-4P in-ears that have never been driven by an amp that could certainly use one. Thus I am most interested in an amp that could probably fit in my pocket, for example. In the future I'll look into a desk amp/DAC combination but I'm not quite there yet.
I primarily listen to classical, but also regularly listen to down-tempo electronic/trip-hop and so good bass performance would be nice as well.
So I'm looking for a recommendation for both a pair of circumaural cans that would be great for that kind of music, and a portable amp that can adequately drive those cans along with a pair of Etymotic buds I have already.
Just to get the conversation going, I'm heavily leaning towards the Sennheiser HD 600, but I am willing to hear arguments for/against them or another pair.