Wow.
I got these on craigslist lightly used (I think he said like 40 hours of use or less) in the original package and original everything and in perfect condition for $250. Half off is a blast. If I didn't get this good of a deal I would have got the HD 598s.
These are 300 ohm headphones so you need a headphone amplifier that is a given; Luckily, my MSI Gaming 6 has 2 headphone amplifiers built in and can handle 500 ohm headphones; I had the Oppo PM3 planar magnetic headphones before this.
These do feel a little fragile, so for $500, they should maybe have a little higher build quality, but I doubt I'll break them; Maybe that is why these are so awesomely light weight; Just be careful