If money is not a concern and you want the best possible quality on portable iDevice set up, I'd suggest you to take a look at the Cypher Labs Algorhythm Solo (CLAS) or the Fostex HP-P1 as DAC. As for amp, it depends on your needs and earphones.
I have not heard any of those two DACs, but the people here have had great words for them. One downside is that you cannot use them as USB DAC, like some other devices. If you don't mind slightly clunky UI, you can take a look at the HM 60X series, perhaps the 601 or 602 if you need an USB DAC.
Or just go for a simple LOD + amp set up. You see some of the recommendations here, but don't trust the review 100%, go check around the forum too: http://www.headfonia.com/the-usual-suspects-12-portable-amps-compared/
The Fiio E7, E11 and E10 looks promising. I have not heard all of the above, except the Pico Slim which I sold, and might buy one again as new player is coming in. I am using the Arrow amp solely, and it's pretty solid.
