Extract Multiple Audio Tracks from video

iMovie '08 will allow you to "pin" multiple audio clips to video clips or a single audio clip to the background if they are in a supported audio compression format. Your main problem may be properly synchronizing it with the video. As to audio embedded in the video, it will probably be handled as a single stereo track rather than two individual tracks. You can of course, always extract individual channels using QT Pro.

Basically it is the QT Player application with the editing features "unlocked" for use. Apple charges about $30 for a code the will "unlock" a number of features (export of content, adding of tracks with or without scaling to other tracks or selected segments, the manipulating/setting of QT "properties" to include layering of audio and video, dimension scaling & placement of video content for display within the player display area, setting of audio channels, extraction/deletion of individual tracks, etc.). The features are very handy for "light" editing, creations of certain effects, conversion of content, and such. Some users would never have a need for it, others find it indispensable.
Here is a link that may give you some idea as to what it can do: QT PRO VIDEO TUTORIALS