My portable source is a MacBookAir 11inch 2011 playing ALAC via Decibel.
My portable headphones are Earsonics SM3.
I listen most to Rock, Hardrock, Progressive, Pop, HipHop and Jazz (relevance descending order)
What should I put between the source and the headphones to improve sq and keep portability (low weight, battery power). I already have a nice desk setup, so let's not go that way.
Money is not a restriction.