Saw this now. Honestly, I love both and can't pick a winner.
Bass - goes to the D2000. goes lower and sounds deeper and harder. X1 rolls off quicker and the bass is more fluid than solid.
Mid-range - goes to the X1. although it's warm, it sounds very natural. voices sound great though they can be a bit thick. very present mids. d2000 has recessed mids. they sound clinical rather than lush and warm.
Treble - goes to the D2000, lively bright treble but non fatiguing at the same time. rarely sibilant. the X1 has subdued treble. they sound good and natural but I wish they had a bit more sparkle. you lose out at some details due to this. its never sibilant though.
Soundstage & Instrument Separation - this is where the X1's absolutely beat the D2000. due to the open design and overall signature, you can hear every distinct sound separately. as opposed to the d2000 where many sounds mush together to give it a more "full" sound. positioning and imaging is also better on the X1, greatly due to the open design I think.
Comfort - tie - maybe a small edge to the X1, both are comfortable. X1's can get you itchy ears after a while. D2000 can get you sweaty ears after a while. headband is better on the X1, so is earcup space. overall can use both for quite a while. I have a small head though and wear glasses.
They compliment each other well. Probably the best open and closed headphones in the ~300 range for non-extreme bassheads. I also have the dt770 which does a few things better but they hardly get use since I got these two.
Edited by canuckavelli - 5/3/14 at 4:04pm