I don't really mean to start an off topic discussion of burn in here, but it's been my observation with every headphone that I've ever bought that the headphone sounds better to me over time regardless of whether burn-in is taking place or not.
ie: That I've listened to things that have already had enough hours on them to be fully burnt in, but it takes me a while to listen to enough different types of music on it on it to really get a handle on how they sound beyond the initial things that really jump out to me.
I've listened to things and thought "wow this sound really" changed, and then subsequently tried a brand new pair or had a replacement pair and heard no difference.
I always compare it to wearing a new pair of glasses. The glasses don't change; your brain does.
I can definitely say that I like the AD900X's more than when I first tried them, especially since the fit is better. I'm more inclined to attribute that to me getting used to the way they sound more than anything else.
What I'm trying to figure out is, are they really better than their closest conceptual counterpart, the Sony MA900. To me the sound staging sounds like the same way the AD900 and AD2000 sounded to me after many, many hours of operation: wide, airy but actually somewhat flat in the way it placed instruments. This is not something you would really notice or care about if the ATH-AD900X was your only can.
I'm doing A/B's of the AD900X at the same time I'm switching between things like the MA900, GR07, 7550, XBA-40, etc and they all do a better job of conveying the physical feel of instruments in space and delivering a well formed bass response. I suspect this actually comes down to the AD900X not being able to deliver fantastic transients - just like the AD900 and AD2000 which I liked but eventually passed on.
I want to be as critical as possible Dsnuts. I appreciate your enthusiasm but you sustain the same level of enthusiasm for a lot of things you try and its honestly hard to believe that everything you try could be that intensely good. The AD900X sounds excellent and for the price point the build quality and sound quality are wonderful, but it isn't a perfect do no evil headphone.
It's an easy recommendation but at a similar price on Amazon.co.jp the MA900 is a better all-rounder. And much more comfortable to boot!
I'll do a few days more listening and then hopefully put up my final impressions :3