Just want to say...fantastic choice!!! I got the HD555 about a month or two back as my chosen headphone for entry into the high-fi world (upgraded from my stock iBuds). They are truly great headphones - impressive sound and just as comfy as everyone says (you will quickly forget that they are even on your head).
With my pair, straight out of the box my first impression wasn't exactly "wow" sound quality. So much that the difference to my iBuds was not even distinctly huge. But after a month or so of fairly regular listening, I have got to say that they have really opened up and sound unbelievable. The sound is so clear, detailed and refined. I listened to my Ibuds the other day after several weeks and I was shocked by how muddy and veiled the same music sounded! The difference is certainly very clear now and the HD555 is worth every cent. So, you may want to burn-in your pair for a while to get the true sound quickly (The burn-in sticky is helpful).
Have fun and keep us posted!