'm thinking about getting the
DT990 Pro 250 ohm Headphones to use strictly for gaming, since most of
the reviews I read and viewed they are perceived as very good gaming
headphones since it has a high bass and all. And I also will be getting
the Fostex T50RP MK3 (modded) for music or maybe the DT 880s?
As for my question, will the Schiit Magni 2 Uber + Modi 2 Uber be able to drive both of these headphones?
Thanks in advanced 
Yes. Easily.
Yeah, I think it's a 'Yes' to every question you've posed.
DT990 = Yes
T50RP or DT880 = Yes to both (although you'd notice a bigger difference between T50RP to DT990 than DT880 to DT990)
Schiit Stack = Yes (Schiit Stack should be able to power just about any headphone out there)
I think there is a far more elegant solution.
For the same price as all of that, you could simply get the sennheiser HD600s and a parazound Z dac.
It will suit your gaming and music needs while being a much higher quality system for the same price.