How loud do you listen? The sensitivity on those might necessitate a little more power than a normal situation would dictate. Those lower power portable solutions might start clipping on you if you tend to turn it up.
This one would be my vote for the portable solutions, at ~150mW of power to play with, give or take.
This one should also have enough power for a comfortable range and headroom, but I think the NX4 measured a little better and is overall the more versatile option.
Otherwise, check out Amir's
Master List if you want an idea of other options.