weird... i have at home Ipod touch 5G, iPhone 4G, Cowons and C3. of all C3 sounds smoothest and bests any of iPods, iPhones or Cowons... what you really do not realize during first listen how much C3 changes sound to bring stage and layer detailing properly. many concentrate on artificial warmth and richness while this comes at expense of losing naturalness and digitalization of sound.
i think you must experiment with various IEMs and also consider BH amp which will re-open whole music nirvana to you.
i just cannot believe we have different C3 and iPhones/iPods... what i admit none of iPods or iPhones we have is modded or rockboxed... but i doubt this will change much in listening experience because what C3 brings is lucidity, stage, detail layering and fairly neutral yet analogue sound and black space background.
i can imagine iPhone sounding meatier more pleasing on first comparison but the more you will be going forth and back the more you will be willing to listen to C3.
for me iPhone could not match any of my Cowons which are much better players and C3 knocked all my Cowons out of water.
all IMHO and based on first hand experience.