First one would need to know the reason you want to upgrade.
Otherwise if you have had no issues with quality at the price range for that headset you currently have wouldn't just something like this work.
I'm perfectly happy with the HD600, but I wanted to see if I could tell any difference with higher end headphones. So I figured I'd buy 5-7 better headphones to see what they were like.
Yes, as a Sennheiser fan, I figured I would get at least the HD700 and HD800.
I'll put my vote in for some planar magnetics, HiFiman specifically.
How does the HiFiman stack up against the Audeze LCDs?
thays what they call a myth....We need yo know what you are driving them with. At that price you start pairing more than just headphones or you wont tell the difference of your hd600s.