I've a pair of Sennheiser HD 600 (previous
generation, got replaced by
the 650 not long ago) and they are extremely clean. I learned to trust
them almost completely: if the HD 600 doesn't reveal it, it either
doesn't exist or it doesn't matter. Also, they don't "color" the
sound;
what you hear is what is actually on the disk.
Something like an HD 580 (previous generation from the 600) might
collect dust in a corner and might be had for like $100 - $200 if you're
lucky, and should provide very good quality at an excellent price.
And how is the
HD 570?