I finally got my HD-558 in the mail. I think they still need to be broken in because they don't sound as good as everyone is claiming. Don't get me wrong, they sound good and they have an enclosed design which is comfortable and filters ambient noise out. But music doesn't sound as real as it does on my Grado GS-1000.
I realize now that you really get what you pay for with audio equipment. I spent 1/5th the money on these as my Grados, so of course they don't sound as good. However, they definitely sound much better than 1/5th as good. I would even say they sound better than half as good. The value for money is amazing, I do believe that these are the best headphones in this price range.
I will take a few months to break them in, my Grados didn't start sounding good till about a year after I bought them. Listening to these headphones makes me realize how spoiled I was with the Grado headphones.
However, I can tell the build quality and durability is far superior to my Grados. I only bought theses because my Grado headphones kept falling apart and I can't listen to music on the go, and with convenience.