Wow, this thread is really quiet.
I have been meaning to post this but here are some small impressions from others at a recent meet in AZ with my ad2kx's: http://www.head-fi.org/t/672341/az-summer-2013-meet-impressions
The ad2kx's can sound great out of most any sources. I know this is something that we can infer from them being very efficient, low impedence phones but I really do mean it when I say they sounded pretty killer in my time with them straight out of an iPhone 5 and good source material.
Out of the GS-X (single ended), and the Lynx Hilo + laptop as the source. I found the sound to be incredibly neutral yet still deeply resolving with details. This was too much of a good thing IMO and didn't do the ad2kx any favors; I walked away almost preferring the iPhone. Throwing the ad2kx on a tube amp like the Eddie Current Balancing Act or the ZDT is significantly more enjoyable of a listen in my book.
I don't doubt that my experience with the GS-X so far is very dependent on source rolling; as of right now I simply do not have a ton of sources to swap at my disposal but that will be a different story in the next few weeks.