I'm having exactly the same issue as this, and tried editing exactly the same configuration file to no avail.
System spec should be able to handle it fine :
Core i7 980x @ 5.25GHz
Asus ROG Rampage III Extreme Mainboard
24GB Triple Channel Corsair Dominator DDR3
2x Palit 3GB GTX580 (SLI)
3x Dell 2408WFP 24" (Portrait 3600x1920)
Really disappointed tbh, a lot of friends have been talking about how awesome the game is, and I really wanted to play.
Funny enough, if I disable SLI and set my displays up in landscape mode, the game will work fine at 1920x1200@50Hz. I just don't feel like breaking my neck playing it sideways, or re-arranging my desk every time I want to play Dx.
Edit :
I've taken a look at the error log that the game produces on crashing, just a one liner that gives no real help :
[16:36:12] MAINAPPLICATION mgEngineDx.cpp ( 352) Error Failed to create D3D device : Unable to find requested mode (800x600@0)