You should understand the difference between an amp, a DAC and product that takes the digital data from the Ipod, bipasses the Ipod's lower quality internal circuitry and uses a separate higher quality DAC then sends the superior analog signal to an amp. Some amps have built in DAC's, like the RSA Predator or a variant of the TTVJ Slim, but they do not extract the data straight from the Ipod. These are more of a convenince for running audio from a lap top via USB cable. So the term DAC is used in different ways.
I would stay away from the iBasso line. Their build quality is improving but not as good as the RSA, ALO, TTVJ or Pico lines. Though I do like the opamp options with the iBasso. I would read a good site like headfonia.com and see their evaluation of many amps, but maybe more importantly the way they describe the sonic signature of different amps to find the one that will deliver music that fits your preferred audio tastes. This is a much more important base for choosing an amp than PRaT or Dac's or whatever.
The biggest gain you get using an RWA IMod, Fostex HP-P1 or Cypher Labs CLAS is an upgrade in clarity. The amp still has a big influence on the sound after the DAC has done its job. There continues to be more and more money being made in the portable audio market, so if someone can sell a product to give just a bit more quality then someone will jump on it. But in all my tinkering with cables, amps, sources and phones I have noticed the biggest influences on sound are amp and headphones, followed by upgrade in headphone cable. My experience is that trying to get the purest source from the Ipod begins to get into the area of diminishing returns, similar to dropping a lot of money on LOD's.