Hi team, I've been a lurker for a while, but it's time for an intro :)
I have the HD 598 and I like them for the styles I listen to (house, and Eastern European popfolk). I've noticed they aren't that great for deep bass rap, at least without an amp. My onboard cards are working for now. I plan to get a Magni/Modi combo for Christmas. I am also already looking at the HD 650 which have some good comments on being amplified.
One thing I learned here, there is never a "final" purchase for many people. Everybody constantly tries to upgrade, and I think I'll fall to that pattern as well. Happy listening.