Adding an Audio Track in DVD A

I'm trying to add an audio track to my DVD project.
I would like to select this audio track as an alternate audio source while watching the DVD.

I have the main video/audio in my project, and when I have that selected in the timeline, I can see the audio & the video tracks.

But no matter what I do, I can't seem to figure out how to add another audio track.

I've rendered a seperate ac3 audio file, and tried inserting, and dragging that file into the timeline, but it never shows up.

Any tips on where I'm going wrong?

Brian
DVD a 4.5