If you have a good set of earphones and want to improve the sound quality from an iphone, here is a great bundle to consider.
The dac is DDHifi TC44A, ultra portable lightning connector dac. It has a 4.4mm output and uses a high quality dac for great audio quality. Fiio LC-RC replacement cable has mmcx connectors to the earphones and swappable plugs, including a 4.4mm plug for this dac.
If you have been using the apple 3.5mm dongle, with a good quality set of earphones that has mmcx connectors, use this upgrade cable and dac to enjoy improved audio quality. Its a great way to breath life into a set of IEM's.
Headfonia.com said this about the dac: Sound quality is surprisingly good, build quality is top-notch... the conception design makes it the perfect companion for your iphone.
There is an even higher end cable available as well, that has Pure Silver wire to bring out more detail in the highs.