ok, well i'm listening to my 580's right now with the oehlbach upgrade (btw, lindrone, Tuberoller did a great all inclusive cable review, too lazy to find the link
)
and the cable upgrade makes a signfigant difference (but i got mine for 35 bucks!). I think the bass is much tighter and the overall feel of the thicker cord is much much more reassuring.
even if it's just psychological it seems good to me!
with all this said, i have decided to sell my 580's and upgrade to the 600's. I simply don't have the cash to buy the 650's and i demo'd the 600's in nyc this past weekend.
the 600's are better, much better. the carbon fiber housing makes the acoustics much cleaner, tighter and clearer.
i'm really not good at pinpointing in words what the sonic differences are, but i trust my ears and the difference was enough for me to switch.
i think bass was a big deal. high and mid bass were so much better on the 600's.
withall this said, the 580's are wonderful, out of the ms1's, akg 271's and 580's, they are my favorite and the only pair that i would have stuck with...if not for the 600's