Esoteric N-01XD SE vs N-01XD

I am looking to upgrade from my N-01 to the XD DAC technology.   I like the sound of mine and the soundstream music player, but the XD DAC technology sounds like a good step up.     

I would buy a used N-01 XD unit, since I know this is not a field upgrade, and i now see there are a few used N-01 XD SEs available.   

Anyone have experience with the N-0XD SE and what is the upgrade over the N-01XD?  Theres about a $3k difference in used pricing between them, so i am curious if it's worth it.

How long has the N-01XD SE been out?   

Am I seeing used ones because the N-01 line is due for another model upgrade soon?