In terms of planar where the sides are tied down, the center will flex more (different amplitude), but will still excite at the same frequency as the sides which flex less (less amplitude but at same frequency). This is why I'm not so sure about the differential damping schemes.

Didn't get you there. If there are areas which emits waves of different amplitude, then  different amount of damping may be needed to control those areas to the same degree.

I am not myself a big fan of 'differential damping' these days but the general reasoning seems to be quite logical to me.

It would be interesting to see how much the He6 measurements would change if they were powered by an ipod.  I'm curious if resonance artifacts can ever be changed by amp/source even in worst case scenario like this. 

Hopefully this isn't too off-topic, but I was wondering how you guys would compare the HE6 vs HE500 or HE5LE?  I've only heard the HE6 and HE500, but the listening sessions and amps were both different.  I tried wading through the main thread on the other site but there's way too much noise.

Also, any experience on the velour vs pleather pads would be good to hear.  If the pleather pads are much better, I'll pick up a pair with a new replacement headband.

Hopefully this isn't too off-topic, but I was wondering how you guys would compare the HE6 vs HE500 or HE5LE?  I've only heard the HE6 and HE500, but the listening sessions and amps were both different.  I tried wading through the main thread on the other site but there's way too much noise.

Also, any experience on the velour vs pleather pads would be good to hear.  If the pleather pads are much better, I'll pick up a pair with a new replacement headband.

To me.....

HE-6...very bright on the wrong system. Slightly bright on the right one. Very deep, tight and well controlled bass.
HE-500....still slightly bright, can be a bit dark on some systems. Slightly flabby bass.
HE-5LE....fairly neutral.

The pleather pads bring out more bass. The velour bring out more treble.

For the hifiman's, I prefer the velour.

Thanks for the detailed rundown on all three headphones!  I have the opportunity to pick up an HE6 for a nice price and have been looking for a good dynamic standby.  I kind of like the LCD2.2 but the ergonomics and muddiness bug me.  I heard a HE6 through a Trends amp and it was nice, though I didn't listen long enough to make any strong conclusions.  I'm hoping the HE6 does well through an Emotiva mini-X, though it seems to be a crapshoot on how the HE6 will respond to a particular speaker amp.  Unfortunately the folks at Emotiva didn't have any experience on how their speaker amps would perform with orthos.

It still amazes me that a used HE6 is cheaper than the going rate for a used LCD2.1.  I suppose the LCD2 and LCD3 are more impressive upon a first listening, but they give me a headache soon afterwards.