Thanks guys - these look and feel like medium grade pleather to me so hoping that time will do the break in work!  

After a couple months the stock ear pads on my 900x have not softened up - has anybody had found that they end up breaking in?  

LCD-2 rev. 2 is pleasantly growly for bass-intensive electronica.  Definitely preferred over the T-1, which is my other high-end reference.  

  Does the Stratus eclipse the Sonett to the point that you would be happy living with only the Stratus or are there circumstances in which you would put the Sonett to work for certain types of  genre / headphone listening? 

Interesting point on the decreased noise isolation of the A900X leading to a little more air circulation and therefore comfort - hadn't noticed it but could be part of the reason the A900X are definitely easier to wear for longer periods of time, although mostly (for me) due to the wing design.  

Looking for a Bay Area (preferably Oakland / Berkeley) tech to perform some minor modifications to a ss headphone amp.  Any recommendations at all would be appreciated - thanks!

A bit late to this but based on your criteria the A900X would do the job.  The K550 do have excellent clarity up and down but the A990X are more textured and engaging.  

Quick note on finish and materials quality since I have used both the K550 and the ATH-A900X for about the same amount of time now (approx. 60 hours).     A900X plastic ear cups present a fine satin finish that highlights fingerprints and smudges and is difficult to clean.  A900X ear pad...

Thanks, the Shure were not on my radar before, will look into them.  

  Quote:   Fair point but for those of us with zero build skills there are fewer options.  Quick question on a slightly different point:  would a decent variable DC power supply represent an upgrade of any sort?  Would be able to use it with a variety of components as you upgrade, etc. 

Looking for headphones that will help "take apart" small classical ensemble work, i.e., something that locates the players in space, separates the instruments, allows you to distinguish violin 1 from violin 2, etc.  Basically interested in something that excels at stringed instrument timbral...

Using the Purist Audio Design System Enhancer to burn in and seeing improvement for a new pair of AKG K550 after a couple cycles.  It is supposed to speed burn in for all components in the system, including cables, etc.  Others have similar products (Cardas, Isotek) but haven't tried them -...

Has anybody tried the Welborne Labs power supply upgrades?  About the same price as the NuForce...     http://www.welbornelabs.com/pshead.htm