[Darkseth]

   
I've found that some people like having a volume knob at their finger tips
And a Xonar DX/D1 used with an external headphone amplifier makes sense, the Xonar DX/D1 has a 100-Ohm output impedance, so the DX/D1 is not that great for driving low impedance headphones.
And the Schiit Magni (or other external amp) is something that can be used with more then just a Win PC.

- That volume knob is indeed a valid reason
- I used the DX, and tbh, didnt really noticed the 100 Ohm output impedance in any negative way (but that said, i have used the Frontpanel, not the rear jacks). My old Shure SE 215 also didnt sound really strange or anything.
But then again, why combine a 60 bucks DX, with a 80-100 bucks AMP, if you can just get a Phoebus/Essence for that, which both have plenty of power, 10 ohm output impedance (which shouldnt make any problems, if you arent using 16-30 ohm 3-4 Driver BA inears), and a better DAC
Or even the
- If needed. I personally dont have any other source i could use for an Amp, besides my PC. And i think, thats the case for most. And here, i would even prefer an external DAC together with an external AMP.

 

[Gamerhead]

 
- Fiio E10 / E10k~. Quality is compareable to a Phoebus, at a cheaper price. But no software features, no driver problems. Plug & Play. You can STILL have a Surround simulation! Razer Surround. In my opinion, thats one of the BEST software surround solutions for gaming you can get.
- Higher price range: Asus Phoebus (Solo). Pretty much the best of everything for gaming purposes, without any cons (except the higher price).

 
On the Fiio website the recommended impedence of the E10k is 16-150 ohms. The DT990 being at  250 ohms, would this be a problem? From what I've read the setup works fine, but when the manufacturer puts the impedence threshold below my headphones I begin to worry ...

 

[Darkseth]

No, you can completely ignore these impedance recommendations in ANY product.
The more important information, if the output power is enough to drive the headphone is NOT the impedance, but the efficiency.
Several users have claimed, that the Fiio E10 can even drive a dt 880 600 Ohm without much problems.
 
For example, the 250 Ohm dt 990 is easier to drive than a 62 Ohm AKG K701