Don't believe the hype. The SHP9500 is certainly not better than the HD 600. It's not even better than the HD 558.
The reason the SHP9500 is so expensive now is that Philips discontinued it. It was a pretty good value at $50, but at $120 it's a tough sell vs. similarly priced cans like the K612, AD900x, and HD 558/598, which are in a higher tier of sound quality.