This is not a real in-depth review or anything.  I bought the Custom-1's and wasn't quite happy with them in terms of bass.  So I bought the Custom-2's.  For about a week I had both of them.  Anyways, I did a blind study where I had my wife hand me a set of headphones while I had my eyes closed.  I then listened to a song on each pair of headphones.  After doing a song I would write which headphone I thought sounded better.  I did this for five songs (all 192 or above mp3's on my mp3 player with no EQ enhancements).  I tried to do a variety of songs so I could get an overall performance of the headphones.  Please note that I am not an expert by any means.  

The results ended up as this:  I picked the custom 2's every song.  I can't tell you exactly why but they sounded fuller and more live.  I could pick out individual sounds in the songs better I think.  The bass response was also better (less muddled) on songs that featured low bass.

 So I am now returning my Custom-1's and keeping my Custom-2's.  It wasn't like OMG the 2's are so much better because the 1's are also very good.  But if you buy the 2's I think the extra money is worth it.  There is a difference.

They should be, the 2's are more expensive than the 1's and have better parts and tech   I'd love to get a hold of some 3's myself.

The Custom 2's also have dual armatures.  While the armatures are the same having 2 means they don't have to work as hard.  I forget how Professor Thump said armatures work differently from speakers (or maybe pretty much the same) but 2 armatures are going to give better deeper bass and more effortlessly than a single armature.  I think each armature may also be loaded or the housing tuned to optimize one for the highs and the other for the bass.   

Hi Ben,

You are correct that their are two arms allowing each to work less but , you are missing one key area of the design.  We have filed for a patent on Custom 2 (KG532) armature because it is a special hybrid nobody has done before.  The actual moving parts (armature, push rod, diaphragm) are the same in both transducer cans.  The difference is that their is an additional acoustic treatments on one of the two parts yeilding higher bass response and lower THD and IMD.  Now you have the dope but it's not from Hope.  ...Sorry but Dope from Indy just sounds like I am stupid.

Acoustic treatments ... that's the term I was looking for.  Anyway, they sure sound GREAT. And the IMAGE and Custom 3 are even better (so I've been told)