Check the audio section.
But yes, you can change the stock head unit if you want. It will involve either an adapter (to allow the aftermarket unit to work with the Bose speakers) or replacing the Bose speakers.
Many opt to just replace the Bose speakers (a set of newer speakers that will outperform the oem stuff is not much more than the adapter needed to mate the new headunit with the oem speakers).
You will eiter need a faceplate to fill in the remaining space (the oem unit is 1.5 din, most head untis are 1.0 din, so you need to set the 1.0 din unit in a faceplate) or you can get a 2.0 din unit (like the ones that come in the C6 and newer cars). This will require a custom radio surround (basicaly a modified center console bezel, guys make them as a cottage industry).
Dont know what you're looking for, but you can also keep the oem set up and add an Ipod adapter. Several ways to do this. Which allows you to have all your digital media available.