I will indeed do that. Do to circumstances, I can't burn my X1's in as quickly as I would like. I think they may only have about 30 hours of burn in so far (and they are sounding amazing), but yes, I'd like to make that comparison once they are more fully burned in. The AD900X's are amazing off of the E12 though, and have more forward mids/vocals, brighter treble, and larger soundstage than the X1's at this point, but the imaging is not as tight/coherent as the X1's. As of right now, my opinion is that they both rock. But those AD2000X's... I'd sure like to hear them.
One thing that I really like about the X1's is the replaceable cable. I put a cheapo 3' cable on the X1's, so I can wear them portably (the X1's have amazing synergy with the C3 + BH btw). Whereas the AD900X's pretty much have to be used at my computer :(
Yeah the somewhat imprecise imaging of the AD900X has started to really bother me, as I've realized that the WS99 actually has better imaging and articulation of microdetails. I'm hoping that the AD2000X rectifies this problem and also provides more bass. Wish there was a more in-depth review of the AD2000X though, sorta taking a really expensive leap of faith here lol. Your description of the X1 as an open version of the WS99 REALLY got to me, always wondered what an open WS99 would sound like (most likely insanely awesome!)