If I understand your problem right, I suggest you do the following:
1. Create a new sequence.
2. Click on the Tracks tab.
3. Under Audio choose Multichannel for “Master” and 3 for “Number of channels”.
4. Choose Adaptive for “Track type”.
5. Map the audio. For Audio 1, Output 1 is set to 1, Output 2 & 3 are set to none. For Audio 2, Output 1 is set to 2, Output 2 & 3 are set to none. For Audio 3, Output 1 is set to 3, Output 2 & 3 are set to none.
6. Tick “Open” and click OK.
7. Drag your audio sources into the timeline to see the meters.
8. Click on the monitor channels (they turn blue) to activate all of them.
HTH