DarkWolf...
...Since I only know the HD 600 and you only know the HD 590, this may not be of great help for you. I'm a big fan of the HD 600, which, in a slightly modded form (removed foam pad, own cable), I find extremely versatile, and despite all the other cans I own – among them two electrostats – it is the one I use 90% of my headphone time, with an amp that seems like made for it: the EMP.
There are so many different tastes and ways to perceive headphone sound that it's impossible to predict which headphone suits your preferences best, the more so with the tiny assortment of cans you have already heard and judged. Well, you have listed your criteria, which are more or less all the qualities a headphone can feature. And for my taste the cable-upgraded HD 600 or (maybe to a slightly minor extent) HD 580 does have all these qualities. I don't want to disqualify any other headphone that way, but I just can speak for the ones I know, and these are of a limited number. I could highly recommend the ER-4S, BTW, but I remember your preference for an open design, and those are as closed as headphones can be.
The Corda HA-2 you're considering seems to be a very good choice, after the things I've read so far. If I already hadn't the EMP, this would be a tempting offer.
I don't quite agree with
Vertigo in terms of Stax: I have listened to my Archos MP3 player through my own electrostat with lots of pleasure, always aware that there are some restrictions to the sound originating from the mediocre source, but nevertheless the joy was barely restricted, and the transducer's sonic superiority and qualities weren't really compromised. Of course it's overkill and unreasonable in view of the source (although the Terratec supposedly isn't that bad, and MP3 doesn't necessarily mean poor sound at all), but I would rate it as a passable alternative to take a Stax into consideration, if you can afford it – and if you can live with one limitation: electrostats generally lack the extra «energy» for example an SR-325 adds to the music, especially in the bass. It's just you who can judge it, by auditioning... Whenever you have the opportunity to compare a Stax to a HD 600... or whatever other premium dynamic headphone..., use it!
Good luck!
JaZZ