Not quite. HD600 feels like all the frequencies are smashed together. He500 has a lot more detail, air and slightly better soundstage. Soundstage-wise, it's nothing like the HD800, but still better than the HD600.
But HE-500 does have a dip between 1-5KHz, which may be a deal breaker for some. HD700 has a way worse dip around the same frequencies, and that was a deal breaker for me.
Ultimately I feel the benefits outweigh the cons. I'm still undecided. I would definitely get the HE-500 if it were as comfortable as the HD600 though...
What does "HD600 feels like all the frequencies are smashed together" actually mean? Monotone, no way. Other than the roll offs at the most extreme ends of FR, it may have the flattest FR, certainly the mids look like the best in this graph.