I posted in your other thread before I saw this, but basically it does sound to me like the 580's just arent for you... I've heard this complaint about them before, that they are too warm, soft and laid back, and they are all of these things. If you dislike this trait, then DO NOT get the HD650, which are even warmer, softer and cuddlier.
At the end of the day, its your opinion that counts, so plenty say the 590's are crap or whatever, but I always take such opinions with a pinch of salt. I speak as someone who had lots of top of the line headphones, like the HD650, HD580, Beyerdynamic DT880, Sony CD3000, and yet I am currently using and am happy with some midrange Beyerdynamic DT531's, which while I recognise their flaws, are sounding plenty nice enough to my ears, and yet if you ask on an audiophile board which is better... HD580 or DT531, most would probably say HD580, but I wouldnt... in fact I actually persuaded a guy who is well into his Rega / Naim gear to try the DT531 as he found the HD580 boring and he did and never looked back.
Its not really a recommendation as such, just a point: Trust your own ears. If you like em, sod what anyone else thinks. If you are desperate to try something else though, I recommend trying some Beyerdynamics, theres plenty of diversity in the range... the Beyerdynamic DT440 is the replacement for the DT531 I spoke of, and offers a sound that is somewhat similar to the high end Senn's, but less laid back and more fun, faster sounding. Dont cost a fortune either. Then theres the DT770/990, which are very bassy phones, lots of low end energy, midrange takes a backseat though, treble is quite prominent... I wasnt that keen personally, but loads of folks like them, and YMMV. Then theres the DT880, which for me, sounds better than any of the high end Senn's, very smooth, lovely sounding phones, may not be your thing if your into rock music though, but for most other things, they are pretty good... quite hard to drive too though, and I've never heard them on the Classic, but I cant imagine them being all that bad, and they are more forward than the Senn's. For rock you might wanna try Grado's but I can tell you now that they dont synergise that well with the AD8620 opamps. Maybe if you change to the OPA*** amps... then it might be an option, but then the comfort factor might get to you eventually. Then theres the Sony's, I had the CD3000 - very energetic sounding, but somehow quite unforgiving as well, and hard to get them sounding just right.
Or.... you could just stick with your 590's

and if you like em, why not!