Ok, so after a favorable impression at first listen(brief), I did some longer sessions and then some a/b with my original precision hd 850's, my he 400i's and my hd 800's. The thrill was gone. 800's were superior in every way as you would expect... I will start there and extrapolate to the others. I am using an LG V20 source with a Marantz HD Dac1 dac/amp.
The 800's were far superior in soundstage, detail/realism. The placement of voices and instruments was way better and there were audible details in 800s that just weren't there or greatly lacking in the 58xs. Bass was deeper, tighter and flatter, in balance with the mids and vocals. I expected,this but not to the degree I heard it, these 58xs really aren't like the originals at all.
He 400is were also cleaner and flatter from the bottom up till the top end, very similar there imo. The 400is bass was flatter and tighter. I primarily used Heart, Linda Ronstadt and KD Lang with some Yes, Joe Bonamassa and Pink Floyd to evaluate all of these and the 58xs vocals were shrouded and overpowered by the bass which also sounds loose compared to all 3 of the other phones I compared them to. The original hd 580 precision was also better in all areas but the treble region, with the vocal balance being more forward than all the others but not bothersome at all, on some tracks its welcome actually, they can be had used for $100 or less.
In the end I'd say that the hd 580s, hd 800's and the he 400is were all better with more refined, flatter bass plus more forward, detailed mids to varying degrees. If you love the accent on bass, you very well might like these but the silky female vocals are suffering because of it imo. So with the He 400i's going really cheap used right now, $130 - 175 almost everywhere and the 4xxs in the same park, its impossible to recommend these to any fan of detail and accuracy. I wanted to like em but they are not for me. With the 6xxs on the way, I am now wondering if I'm gonna dislike them too, we'll find out.