Thanks for the response but I’m afraid Mainconcept didn’t help. However, I have found an imperfect solution.
I can extract the Audio using Canopus.
I can encode the Video using Nero and set the volume on the track to zero. I can also attach the extracted Audio file to the Video file in Nero. I can then output as DivX and use ConvertXtoDVD to create the DVD.
Quite a lot of work with quality loss but at least it works.