agschmid,
Someone else asked a similar question a couple of weeks ago, but I just saw it and responded yesterday. How to retrieve all questions from a quiz. I think the problem is that the person linked to the questions in the bank instead of adding them to the quiz.
My response was that you can create a quiz where you add all of the questions from the question bank to it and then use the API to retrieve all of the questions. You can also export the quiz through the course export content methods and then use something that opens up the QTI format.
Have you read something that suggests there won't be an automatic migration path for moving to Quizzes.Next? I've heard that there will be, but I cannot put a link to it right now. Or are you just wanting to be proactive about it and move to Quizzes.Next before you're forced to?