I've got the AK100 and while I love it, it absolutely needs the pico slim amp to make it competitive to the HiFiman 901 and even then the 901 has the edge in most categories.
I am pretty optimistic about Sony's entry into computer audio and HiRes DAPs, if they can get me in the ballpark of the 901 sound with the interface advantage of the AK then I am sold. 128 gb is pretty solid although I would love an expansion slot.