The are some recent production of the he4 but it's certainly EOL and I think that the units from Justin are about it. I emailed him about a week ago and he said that he could still get them FTM.
There is a bit more sparkle to the he4 on the treble than the he500 which has a somewhat smoother treble presentation. But understand that the he4 treble is not harsh at all. I liked the jergpads with the he4 while others did not. YMMV
I would encourage anyone interested in the he4 to give it serious look provided that you are willing to put the proper amp with it. It's simply a wonderful hp and IMO outclasses the he400 across the spectrum and yes, that includes bass.