I've just returned to 2.0 FW and the difference between 2.1 is a night and day. Now I remember why I bought DX90 over DX50 and the fact this DAP has two dac chips. Soundstage again is incredibly vast and has a depth(!). I suspect that in blind test I couldn't distinguish DX90 2.1 of the iphone 5s which despite a worse musicality sounds very simiar to the 2.1. I know how it sounds, it's however my personal opinion.
I could swear I hear some micro details with 2.0 I haven't heard with 2.1, WTF? Maybe it's because of different scene creation. Now there is no harshness at all, better separation, better musicality, just another level. ath-a900x gains significantly. I'm just amazed.
Edited by athmospheric - 7/19/14 at 3:03pm