Well, after a 24 burn in period there is a dash more tightness/texture on the sub bass which is all I was hoping for honestly. A few brief impressions here now that I've had a day to absorb the signature.

This headphone is a fair bit better than I had imagined it would be. When I get a new hp in, I typically love, like or hate it. And my opinion rarely changes more than a few degrees from the initial impression unless...there is an amp mismatch or the hp's benefit significantly from burn in. My vsonics changed 180 degrees from about 200 hours of burn in.

 What I like:

 There are two, maybe three, aspects of the x2 that really stand out for me. The first is the performance that it offers in the sub bass. My God is it punchy and tight. This is not "fun bass" aka m50. This is real audiophile bass with texture and does not bleed into the mids. It's linear to the recording which I really appreciate. It was slightly bloomy on first listen but has tightened up nicely overnight. It doesn't have the speed of planar mag bass, which means the decay is a little slow. And it doesn't quite match the texture and full extension of the lcd2.2, but it does put you in that neighborhood. Even on the Crack or wa3 (both with boutique tubes) the hd600/650 gets spanked by x2 on merit of the sub bass. The d5k is the only other dynamic driver hp that offers this level of sub bass, but the d5k was somewhat one note and was not linear...it punches up the bass irrespective of the recording.

Next, the sound stage is impressive. The signature is presented both wide and deep. Instrument separation is top shelf and the presentation just has a nice air and openness that the hd600/650 can not match. The sound staging is the first thing that gets your attention after the luscious sub bass is noted.

Finally, the build quality is exceptional. The x2 reminds me of a tank built by BMW...leather, metal, finely appointed. It's exudes class and craftsmanship. The suede covered memory foam pads are some of the very best in the game.

 What I don't like:

I don't care for hp's with a single exit cable. It feels and looks "unbalanced, unfinished." The black halo that Philips called the headband is some what ridiculous. I look pretty much moronic wearing these and so will you. But you know what, I just don't care.

The mids take a slight backseat to the hd6x0, but it's nothing that keeps me from enjoying vocal-centric music...jazz and acoustic pieces come across with rich smooth mids.

Okay, that's all for now. Another couple days of burn in and then I'll get into some more serious comparisons to other mid fi heavy hitters.

Matt,

Nice initial impressions and look forward to your follow-up. Do you have a clear preference for the X2 over the venerable HD600/650.  It sounds that way as you give the X2 the edge both in sub-bass and in openness airness, quite  a feat.  If I am reading you correctly the Senns only edge out in the looks department. What about versus any of the AKG K/Q series cans, including the recent K7xx if you have heard that.

How hard are the X2 to drive. You mention a bunch of quality amps. Can they be driven well by more modest amps or a smartphone. My view is that while the HD600/650 can technically be driven by an Iphone, for example, and depending on the track may be decent, such a device is basically not adequate for those cans. Curious if the X2 is in the same camp or if you can decent SQ from a phone/tablet.

Also, I believe you used to have the PM-1 and/or PM-2.  How does the X2 compare to those. I suspect that it will win from a value perspective, but curious as to how they compare on an absolute basis regardless of price difference. Right now I am keeping my PM-2 because I really value their easy drivability and portability and was willing to allocate more dollar value, if you wll, to those qualities than I think the PM-2 would otherwise be worth on SQ alone. But if something like the X2 was also easily drivable I could see switching over. However, I assume being larger that they are a lot less portable.  Thanks.