There is a good back way to the Barossa via Golden Grove then Kersbrook, Williamstown, Angaston, Tanunda then Nuriootpa. That would be 3-4 Hrs with a few stops (bakeries).
And by the way I just realised in your poll you had the 13th and 14th so I presumed the 14th was the Sunday which in fact its the 15th. I want to change my vote to the 15th or 22nd.