I received my HE-500 last night and still giving them a good listen before I pass any judgment. So far its neutrality has been very impressive, but I am not totally blown away.
I'm not sure if it is my source (EAC ripped CDs played with foobar2000 > HeadRoom Micro DAC & Micro Amp > HE-500) or that they aren't paired with a powerful enough amplifier. I spoke with Ben Thiede at HeadRoom and he said the Micro Amp should be fine to use with the HE-500.
Would there be something better to pair with these great cans? I was thinking maybe Burson HA-160D or Apex Hifi Butte?