The ESS 9018 is the overall much better DAC. The reason you see a preference over it is that the Wolfson chips are well, colored. Which also makes it it's biggest downfall. Here is a very long video about sigma-delta dacs along with very easy to understand explanations why the recent ESS chips are overall better. If you would like to tame a brightness that you don't like, talk to Jerg about his recommendations towards a fix as he seems the resident HE-500 expert.
big +1 here, i have myself as well.
Thanks brunk for the explanations and the link..I am leaning towards the ESS9018 and NFB 28. I hope someone is out there who have listened to these with the HE-500. More advise on the Audio GDs welcome too