I see what you are saying, but my problem lies with my budget limitations. The HE-500 I would love to step up to the he-500, but unless I am able to spot a decent 2nd hand deal I could not see myself getting them.
As steve2151 mentions below, the he-400 is in some ways the younger brother of the he-500 that provides similar sound with a more affordable price tag. That was my train of thought that lead me to seriously consider the he-400.
There seems to be a consensus that the hd650 cannot be called a upgrade from the hd600.
I might have to look that over and rethink the hd650, but thanks for the useful impressions on both the he400 and hd650.
Putting that aside, could someone suggest some headphones that might give me a more clear upgrade from the hd600 while keeping under $500 (and at the very most $550-$600). I am finding my list/options dwindling unless I were to wait a bit longer to move into a higher price point.
Edit -- Thinking on it, I am perhaps not looking for a clear upgrade due to the budget I have placed on myself but instead just something new/slightly different to replace my old hd600 headphones.
Audio Advisor has a demo HE-500 for $615 and Amazon has a "like new" for $620. You won't be sorry you spent the extra few $ once you hear them.