Based upon reviews, the E9 is a great sounding product for the money. For driving most headphone it seems to be all the amplifier that anyone would need.
If your cans are some of the known power hungry critters like the current rash of planar magnetics, or AKG 701/2, etc. then while the Fiio on paper will do ok, it will run out of gas at about .5W or less when driving a 50 ohm load, common to many of the current planars.
Depending upon the type of music you listen to, and how loudly you listen, again the E9 may be all you ever need. If you're going to be more demanding and want better performance from your orthos, something like the Asgard or Valhalla will provide more robust power. The Asgard is preferred for orthos, and the Valhalla has been given good marks with the AKGs.