How do I disable choice options or the submit button until after slide audio finishes.
That would be very easy if you created custom quiz slides, but I think you are thinking about regular question slides? Easiest way would be to split the slide in a static slide (like an image of the later quiz slide) and the real quiz slide. All objects on the regular quiz slides are embedded, which means they don't have an individual timeline and you cannot just control them the same way as on content slides.
How comfortable are you with advanced features of Captivate? Do you also include Drag&Drop slides in the Quiz?