Starting from version 1.2 of Amadeus Pro it is very easy to add a voice track to an existing music track in a perfectly synchronised way:
Open the music track from your hard disk.
Set Amadeus Pro up to record from your microphone (see also Section 4.1).
Choose Record to New Track in the Sound menu.
If recording does not start immediately, click on the red recording button. This will automatically start the playback of the existing music track.
Give your best to create a beautiful voice track!
Once the music stopped playing, click on Stop. This should add a new track to the existing document.
Play back your recording and adjust the relative volumes of the two tracks by playing with the Volume gliders.
If you want to mix the music and the voice into one single track (this is optional, but recommended before saving to an AIFF or Mp3 file), choose Flatten Document in the Sound menu.