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.
It sounds like you were just listening to them at different volumes or with different equipment. The HD 580's upper mids aren't that loud at all. The HD 650's have more upper-mid presence.