You can export it to Animation Codec, this means that video you are exporting will be lossless quality, then in Soundtrack Pro you can add your sound and export it with compressor again without compressing your video. There is an option to just add sound to your video. Then in DVD studio pro you can set bit rate to what ever you want to render your final DVD. Look this is how I would do it, there are other work-flows but I prefer to use this one. Bear in mind if your video is long bringing it with animation codec to Soundtrack Pro will slow down your plyback speed. You can export to 90min best video, this however does not give you always best quality to my experience. Try getting a bitrate calculator if you want to export it via this option.