I was able to get my video the way I wanted using AVI-Mux GUI. However, it's really annoying to render the video with 1 audio stream and also render each additional audio stream separately and then stitching them together to form the final multi audio AVI. It would be so nice if this could be setup with Vegas and then perform the rendering in 1 or even a couple steps. Hopefully someone knows if/how this can be done.