1] In your mixer, pan the first piece (1&2) as a normal stereo track of music, hard left and right. 2] Next, pan the second track (3&4) dead center for both channels. This will make the track mono. 3] Now phase reverse both channels of 3&4. If you kept the tracks sample tight, when you play, you will only hear the stereo information - anything common to both channels (mono) will go away. If you bounce this resulting output to a stereo file, you have the side information isolated for further processing (we'll call this 5&6) . Now, if you mute 1&2 (leaving only 3&4 in mono and phase-reversed) you can bounce this resulting output for your mono information (we'll call this 7&8). If you line up the 5&6 and 7&8, they'll recombine, giving you your normal stereo output.