FlipBook lets you have up to 3 different soundtracks in your scene and all you have to do is drag n drop to get them there. To sync the sound with the animation just drag the sound up and down in the xsheet by holding down the Alt key.
You can also import your sound by clicking on File > Import > Sound. Once the file is in the scene, FlipBook let’s you sync any point in the soundfile to any frame in the scene for total control. Just open the sound dialog by right-clicking on the header at the top of the level and enter the frame # in the scene and the point in the sound file (measured in seconds) that belong together.