Well..the HD-580 doesn't sound like the 600. Very similar and same driver. The grill changes the sound a little. HD-580 is very musical to me. The HD-600 less so..(for me)
Neither are perfectly neutral IMO. I would say the HD-580 is slightly more colored due to it's more forward upper mids and treble.
This is the only reason it's a little more "fun" for me.
Someone is a genius if they can tell me why my HD-600 makes my garbage tracks sound better than they really are. Isn't that itself a coloration?
My HD-580 makes my garbage music sounds like garbage and the HD-600 doesn't. I won't say anything..
BTW the upper mids on the HD-580 can often be somewhat fatiguing. Much more so than the HD-600.