I was really down to the K553 or the ON2, but for the amp/DAC I was wondering if something like a Fiio e10k would be better than something like the Schiit Fulla or other amp/DAC combos.

I'm looking to get some nicer headphones and an amp/DAC for use at work in an office environment. At home, I use Beyerdynamic DT990 Premiums, a "starving student" amp, and a Schiit Modi 2. I'm looking at headphones like ATH M50x, AKG K553 Pro, and Thinksound ON2, so something in that price range...