Hi everyone,
 
I have a I question about what would solution pair best with my Beyerdynamic DT-990 600 Ohms.  My usage is approximately 70% music, 30% gaming -- LoL, Skyrim, occasional FPS.
 
I'm currently considering a few options.  Feel free to add other suggestions to the mix.
 
Xonar ST or HT Omega Claro Halo  - I know that the built in headphone amplifiers are rated to 600 ohms, but would they "properly" drive the DT 990s compared to a dedicated amplifier?  If they will drive the cans fine, does anyone know the difference between the Xonar ST and Claro Halo?  Which would be best with the DT990s?  I am also considering the STX since ST's seem difficult to find nowadays (unless I can find someone selling it used), but I hear that the ST has a better sound signature.
 
Xonar DX + External Amp - I would probably pair the Xonar DX with something like a Fiio E9 or Objective 2.  Would this solution be better than the sound card alone?  Since my desk is not too large, it is nice not to have a ton of desk clutter with an added amp, but the E9 and O2 are quite small so it wouldn't be a huge deal.
 
Thanks for your help!

The FiiO E9 is actually very similar to the built-in headphone amplifier of the Xonar ST, and maybe also the HT Omega card (I am not familiar with those, but some of them do use the TPA6120A2, like the E9 and the ST).
 
For the DT990-600, the O2 and the Xonar ST/STX both perform similarly, and should work decently, so getting the ST or STX is a simple but good solution for those particular headphones. On the other hand, the O2 is better than the various TPA6120 amplifiers when driving lower impedance headphones and IEMs. The Xonar DX + O2 setup also has the advantage of modularity, you could use the amplifier separately from the sound card.
 
I would not worry much about the difference between the ST and the STX.