[dgiles]

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. 

 

[georgelai57]

Basically there are 3 types of signal that you get from your iDevice. 1) Amped signal from your heaphone jack, 2) Line out analogue signal that you get from your dock which feeds usually to a standard audio mini plug which needs to be amped and 3) A digital LPCM signal that you get from buying a license from Apple to decode this signal which comes out from the dock and terminates in a standard USB plug.

This third type bypasses the use of any audio functionality of the iDevice and instead just uses it as a mass storage device to feed out digital signal. The signal is then processed on a DAC chip located on a (HP-P1, CLAS, Wadia 170i, Onkyo ND-S1, etc) which then gets amplified etc. The whole point is to bypass the onboard DAC chip of the iDevice and decode this signal using a higher spec setup for better sound quality.


iDevice decoding from above mentioned hardware is not compatible with standard PC USB output and so they are mutually exclusive devices.

One year later and I hope you can expand on your answer. When I want to use LOD on my iphone5, I connect a "normal" LOD (30 pin - 3.5mm) to the Apple lightning/30pin adapter then to the iPhone 5. I know of course I'm getting an analog signal (I'm not that slow) but tell me, has the original digital signal from the iPhone 5 been "analog-ed" by the Apple lightning/30 pin adapter? Or put another way, where is the digital signal converted to analog? Within the iPhone 5, or within the Apple lightning/30 pin adapter? Thanks.