Best choice would be DT990. But not 600 ohm, because E9 wont drive it properly. 250ohms instead. If you use it for gaming, best would be getting a soundcard like Asus Xonar ST, which will sound better than E9 (with music too), and it will have dolby headphone for games.
But there are too much difference over 250ohm and 600ohm? It´s the same price.
Othert question, I saw that 880 is better than 990 ig games... today I have an AD700
If 600ohm is better, witch amp do you recommend?
I have an Asus DX that i heard that de DAC is similar than ST, isn´t it?