I just got mine in the mail and i have to say, coming from the HD555s, these are MUCH nicer. The bass is more present and tighter..the hi are soo crisp compared to the 555s its amazing. The mids are about the same, maybe alittle more up front on the 555s then the 580s. However, the soundstage seems smaller on the 580s. Also, you can notice these cans want more power...my go vibe is maxed out right now and the music is just a tad uncomfortable. The 555s could go well above the point of being comfortable, basically blow your ears drums in a matter of seconds. However, the 555s are bigger, which might be better for people with HUGE ears. The sound from the 555s are darker so might be a better choice to use them for extended periods of time. The pads on the 580s are also stiffer then the 555s, maybe due to the size. The also seem to have alittle more pressure on your head, this might cause the better bass reponse.
Just intial thoughts, these have alittle burn in them already from the person i bought them from...but hardly enough for a good break in. Im going to put about 24 hours of straight bassey music and about another 72+ hours in normal listening and post back thoughts...
But off the bat...much nicer tigher bass, CRISPY hi's, smaller sound stage...if the 555s put you in the 10th row, the 580s bring you up to 1st or 2nd row. I belive with the amp, the 580s are surely worth the extra money vs the 555's. I almost find myself wanting my 555s back for hours of gaming.