Or does it need another amp to add to is as well.
Also, what would you reccomend the FiiO e5 for £20, FiiO E7 for £60, or the FiiO E9 for £85
EDIT- these are for Koss KSC75's.
You can use it as an amp for music as well. You'll need to have a source with an optical/toslink output to plug into it, and you'll most likely want to turn off the Dolby Headphone DSP when listening to music (that'd be the button on the right side of the Tx unit).
As for how satisfactory it'll be, that depends upon your headphones. I've found the Mixamp actually drives my HD650s satisfactorily for certain games (with voice chat volume turned completely down, and master volume way up). But for listening to music or most movies, I run the output of my Mixamp into a Fiio E9, then let the E9 drive my HD650s. But the HD650 is a relatively tough-to-drive phone. There are plenty of headphones that'd be driven just fine by the Mixamp only, even for music.
-edit- I see you added in what headphones you're using. I'm not familar with the ones you listed, but I'm sure someone here who is will chime in soon. :)