i heard the 600's with a graham slee headphone amp i think, they were really nice, but i honestly never heard much of a difference between them and the 598's apart from a slightly more open and ever so slightly more detailed sound. as for aesthetics i will always buy a product that looks good aswell as perform well. in my eyes the 600's are dog ugly

and for headphones, they spend 80% of their life on a stand next to my pc, so they better be pretty ornaments

my point is still that for their intended purpose, and given their price they represent decent value and provide good sound out of less than ideal source material, but yeah, their are alternatives, my favourite is the b&w p5, also incredibly well made and rather good looking.