I bought a couple of these for the exact same reason: i20
The beauty of these little docks is that that take the raw signal from the iPhone (iPod, etc.) and feed them out through either RCA or Toslink. Although these docks are far from "audiophile" quality, the sound is much, much, better than anything that goes through Apples internal circuitry and out the earphone jack.
Did you know that even though iDevices can't play WAV files, you can put them on your device and this dock will output them?