I just got my pair today and right out of the box they sound very good. Coming from my Auzentech Forte to my Matrix M-stage, there is this fullness to the music. I love it. It makes my K501s seem anemic by comparison (they are probably v.1). I love how the 598s can handle pretty much any genre I throw at it. Some White Zombie, a bit of Hans Zimmer, maybe some Daft Punk and then some Pearl Jam. It all sounds great.
The soundstage is really impressing me as well. I have to say, this may be the first headphone I have tried, and I have tried a lot (couple dozen), that seems to get it right. The soundstage is large, but not cavernous like my old K702s. On the 598 some sounds are close like vocals, and others actually sound further away. Yet they never get in the way of each other. I can still pick them out when the music gets going. I think the description brought up a lot in this thread is that the 598s sound like speakers when it comes to the soundstage. I would agree with that.
Now, these are not quite as resolving as say my K501s but they aren't veiled either. There is plenty of detail, it's just a bit... smoother.
The only slight negative to me would be the color. It really is more of a yellowy, creamy color. I mean, once it's on my head it's a non-issue but my wife did call them "70's - tastic"
I don't care though. These things could be bright pink with rabbit ears on the headband. If they sound this good, then that's all that really matters.