I've had the DT-990 pro 250 and SBZ shielded version for a week and I think they sound great together. As far as power is concerned, I can't go up much past 50% which I think would be expected since that card can supposedly handle 600ohm headphones.
The crystalizer of the SBZ pro-studio software works pretty good with the DT-990 for games really brings out its theatrical sound signature. I haven't been able to master the surround functions as it's accuracy most likely drops having crystalizer enabled. I also enable the bass boost for gaming at 45% and a 50hz frequency For some reason at 10hz I don't hear or feel anything extra,... I think it's because the way the bass boost changes the level of the midrange.
The EQ works good too. I drop the two highest frequencies by -5db and -7db to keep the treble "harshness" down at least until I adapt. These headphones have a lot of texture at high frequencies I don't think I am used to hearing. With a 5-35khz frequency response, they sound very harsh to a guy coming from a top end of 25khz.
For music and everything else, I turn off the prostudio and only utilize the EQ. My only real problem is the sound leakage, esp the treble,... but for me it's only been a problem with music.
Overall, I would definately recomomend this pairing especially for gaming.
Though I have very, very limited experience, this pairing is IMO the lowest acceptable budget level for audiophile gaming at $150 for the DT-990 Pro 250 and $70 for the SBZ. I tried spending under $100, Gemini HSR-100 and Asus Xonar DG, and was massively disappointed. Not because they sounded terrible, but because it wasn't what I imagined audiophile quality to be.
Cheers.