So the HE400 would be a step up from the dt990 and would fit my criteria (besides being hard to drive)? Sorry to pester with so many questions, but I won't be able to listen to the headphones before buying them and would like to maximize my purchase. I would like the best I can get for around $500. The dt990 seems to fit the bill, but if there's anything better please let me know.
To be honest I am not really familiar with Hifiman and planar magnetic headphones in general