[ThePolishPaczki]

Which has a better more accurate sound stage? Generally better for gaming?

 

[Monsterzero]

They both are pretty decent for gaming,but if youre into FPSers and looking for an advantage,I'd look into the K701. The + bass on the X2 & DT990 can drown out footsteps at times.
I own all three.

 

[PurpleAngel]

Which has a better more accurate sound stage? Generally better for gaming?

It might help to know what sources (PC, gaming console, DAC/amp, etc) your going to be plugging the headphones into.
As the Fidelio X2 is an easy to drive and low impedance (30-Ohm) headphone and the DT990 250-Ohm is slightly more power demanding.

 

[ThePolishPaczki]

I'm gonna be using a fiio e17k for the dt990s

 

[PurpleAngel]

Which has a better more accurate sound stage? Generally better for gaming?

Sound Stage usually refers to as a 2-channel audio signal source (music?)
Surround sound is the term normally used for sources with 6-channel (5.1) or 8-channel (7.1) source (games or movies).
So I'm assuming your asking about headphones for surround sound gaming (FPS gaming).

 

[PurpleAngel]

I'm gonna be using a FiiO E17K for the DT990s

The FiiO E17K is a USB-DAC/amp (with S/PDIF coaxial input) and comes with zero headphone surround sound processing features.
If something takes the surround sound audio (6 or 8 channel) and process it into 2-channel headphone surround sound,
then that signal can pass thru (USB or coaxial) the E17K, on to the headphones.

 

[ThePolishPaczki]

A lot of games are already made to be stereo, so i feel with the neutral stage created by the amp/dac, the positioning will be really good in games, question is which one.

 

[PurpleAngel]

A lot of games are already made to be stereo, so i feel with the neutral stage created by the amp/dac, the positioning will be really good in games, question is which one.

With the Fidelio X2, you have something that will easy work with your smart phone.
For FPS gaming, I would go for the Audio Technica ATH-AD700 or ATH-AD700X (buy used off eBay), the AD700(X) are very bass light, so not as good for music and movies.
Buy a second headphone for music and movies