Why bother with the E07K at all?
The iPad actually has a pretty well implemented internal dac and amp, and the brief listen I had with my wife's friend's iPad confirmed to me that it is perfectly OK straight out of the headphone jack. More than OK IMO - actually pretty good.
The 225i is low impedance, high sensitivity, and doesn't need amping. IMO - it gains nothing from being amped - except extra volume which you don't need.
So save yourself the hassle - and listen to the 225i straight from the iPad.
If you want to EQ - consider going software (apps like Equaliser or Accudio Pro) instead of a hardware option.
Not sure about sound difference between the FiiO E07K and iPad 2. But indeed, the iPad2 does have some excellent DAC/amp in it. I like it better than iPhone 4 and most iPod. My sister's iPad3 are even better thought but just so slightly not as huge gap as day and night.
Side note: I am actually using my iPad2 as my portable rig with the iPhone 4 for backup only.