I don't know the scope of your project, and this doesn't answer your question, but I'd like to throw this in there just the same.
If you are already getting a DAT recording from the soundboard - you've got the soundboard audio covered - and having the same audio on the videotape isn't going to add much value to your project. What I would do is get another mic, plug it into my camera, and record a second audio source that way. Of course, it won't sound nearly as good as the soundboard audio. However, combining it with the soundboard audio can really produce a nice result. The soundboard audio won't have any ambience or crowd noise - both of which are important elements of a good sounding "live concert" recording. You can adjust the volume of either audio source in your NLE when you're editing the show for DVD authoring. I usually reduce the audience recording audio several decibels so that I still get the ambience and crowd noise - but it's buried in the background and the soundboard audio is what really stands out front.