Are you selecting the second/third/fourth audio tracks in your media player on playback?
Separate tracks are NOT played concurrently. With that setup you will only hear one source at a time, depending on the Track you select in your media player.
Think of Tracks like different audio languages on a DVD. If all of them played at once, you would hear every language at the same time.
You may want a Mixdown track. Check Track 1 on all of your sources, and then a second track where only that source is recorded. For example, I have my Desktop set to track 1 and 2, my Mic set to track 1 and 3, and my alerts set to track 1 and 4. If I want to hear everything, I choose Track 1. If I ONLY want to hear my Desktop, I choose Track 2. If I only want to hear my mic, I choose Track 3. If I only want to hear my alerts, Track 4.