MORE BLOG-ISH CRAP
Turns out that maybe the K501 is the headphone for me. It has none of the problems that plague the K701 (thinness, lack of euphony, crappy rendering of cymbals and similar [well, the K501 has its own inaccurate version of cymbals and similar {I'd say less "shiny" than what is real, and a little darker}, but it is much preferable to the K701's crap], exaggerated sibilance, lack of dynamics, lack of bass, to name a few of the K701s flaws). Near-perfectly balanced sound - not bright, not bassy, not thick, not thin. And the surprising portrayal of POWER; there is a strength here behind the music that I don't hear in any of my other headphones.
The lack of flaws (that I care about) is refreshing after sticking with the K701 for so long. This headphone is superior, IMO, to the K701 in every way.
No, I didn't just buy the K501. I've had it for several months now, but did not use it for the last couple because I thought the K701 was preferable (I was probably trying to force myself to prefer the K701 given that it cost me 3 times what the K501). What got me to try the K501 seriously again was my tiring of the K701's numerous flaws. The K701 is the most flawed "good" headphone I have heard yet. The K701 seems to have been made to ruin the experience of music-listening.
I'm still curious to see what electrostatic headphones offer, so I'm going to get a Stax 0205 system, but I am where I want to be with dynamic headphones.