There is nothing easier than editing a song from your iTunes music library: simply drag it from iTunes onto the Amadeus Pro icon in the dock.
In order to add a new file edited with Amadeus Pro to your iTunes library, the easiest way is to either use the dedicated Export to iTunes Library function from the File menu or to drag the file from the Finder onto the iTunes library.
Warning: Apple does not allow third parties to read protected AAC files. Songs purchased on the iTunes Music Store can therefore not be edited with Amadeus Pro, unless they were purchased from iTunes Plus. The easiest workaround to this situation is to burn the song to a CD with iTunes and then to open it from the CD with Amadeus Pro.