DVD uses only MPEG-2. If you bring anything else into DVD Studio Pro, it's going to convert your media files to MPEG-2 elementary streams during the authoring process.
What you should probably do is just export native Quicktimes from your FCP timeline (since you're shooting AVCHD, your FCP timeline will be ProRes 422), then bring those into Compressor. Apply one of the DVD presets that best suits the total amount of material you want on the DVD, then take the resulting elementary streams into DVD Studio Pro for authoring. That'll give you the best result possible without third-party software or time-consuming manual tweakery.