Davidsh and I actually talked about this and we made sense of it mostly.
(read this post and onwards) http://www.head-fi.org/t/646812/hifiman-he500-he400-jergpad-mod-v2-0-new-revised-feb-28-2013/600#post_9312100
Here's the "too long, didn't read" summary:
Blue = stock velours, Green = jergpad pleathers. Notice the 4kHz~8kHz region where stock velours have a massive dip, and the jergpads fill in mostly? That's the upper mids / lower treble region, and the fact that it is filled in is probably why you perceive more energy there (aka "shout").
It is good though because the FR is smoother because of it, so as you adjust to the new sound signature, the coherency and mids~treble transition is plain better.
Wow, I think that dip is part of why I like the HE500's. My ears are really sensitive to any "shouting" in the mids. I listening to a lot of female vocals where shouting is quite apparent and annoying to me. I think shouting is also apparent with trumpet solos like those of Miles Davis. I remember when I had my Lyr I tried to cure shouting with tube rolling. But, I could never get it right. Consistent with the comments here, when I cured the shouts the bass got wooly, when I cured the wooliness in the bass the shouting returned. This - in part - lead me to change amps. I have not had the same problem with the soloist. I also did not have that problem with my DAC1's amp section. The HE500's really benefit from an amp with a fair amount of power, speed & control (on the low end), and smoothness (particularly through the mid's). The tradeoff is usually pronounced treble - I could live with that.
For the above reasons, I sometimes cringe when I read posts where the HE500's are driven by "compromised" amps. Poor amp matching with these phones leads to a number of nasty artifacts - although the phones still perform satisfactorily. I remember a number of the same problems with full-scale planar speakers with the Magnipans or Quads when not properly amp'ed.