I agree that the HD598's sound better than the M50x. I hardly ever use my M50x. They seem a bit to punchy if you listen to different variety of music. 

I am looking to buy an ATH-AD700 which has now been discontinued and the reason why I'm searching on Head-Fi. I lost my first AD700 on holiday. Whilst here I guess I could ask if I should look for a rare AD700 or move to something better. I use it for FPS gaming. I have come across Head-Fi...