Here is something I posted in the Discovery thread and forgot to put it here:
I have tried the JVC HA-S680 with my Rockboxed Sansa Clip+ (mostly 256KBps VBR MP3s).
Before this, I have never experienced "synergy". If the dac/amp/headphone was good, it was good in almost any combination.
ATH-ES700 sounds very muddy and veiled with Clip+, as both of them are warmish.
HA-S680 is very balanced, so it doesn't have this problem - sounds out of Sansa+ almost as good as out of ODAC+E12.
Ironically, the difference between ES700 and S680 is smaller when playing FLACs through NFB-11.32.
But with Clip+, one sounds like a free earbud you get with any MP3 player/cellphone, and the other one keeps me from doing my job for the past 2 hours.
I was considering X3/DX50 purchase, but I think I'll skip them now.