[MaximumSandvich]

Obviously, since the amp is rated to 600 ohms there won't be a problem with volume (It powers my beyer dt990 250 ohms to hurt-ears levels at less than half volume with the gain switch on and the gain set to 12 db on the e17)
 
I am aware that the Hd800s "deserve" a better amp/dac combo, but I am a college student so as long as there's not a "these will sound like crap now" difference, I'm fine with my fiio combo.

 

[Snag1e]

The E9 should do fine with the HD-800...The main problem with the E9 is its (high) 10 ohm output impeadance...but that isn't much of an issue with a 300 ohm headphone like the HD-800. Why not try it out, you can always upgrade to a better amp latter....

 

[MightyChimp]

http://soundnews.ro/2012/08/30/fiio-e09k-e02i-minimalist-hi-fi/
 
I've looked around the internet a bit. It seems like it should be fine, but you may eventually want to upgrade to a tube amp. 

 

[SgtPepper]

So how did you manage a pair of HD800's?