Exporting more than 2 channels of audio require you to use an MXF wrapper and in the advanced settings of render template, you have to assign each audio channel a bus. Then when it exports it will have up to 8 independent channels of audio. In broadcast, first 2 are the mixdown, 3 may be SOT, 4 is narration, 5 M&E, etc…. But once you assign each audio track to a bus, you can select it on export/render.