I’d agree with Nille here. Whilst doing my post doc, I saw two friends with perhaps mediocre theses go through their vivas. One whose thesis was by far the poorer of the two came out with minor corrections as he did a very good job of defending it, and also impressed the examiners with his broad knowledge of the wider field, and willingness to stand up for his views and interpretations. The second, whose thesis was much better, just meekly sat there and wasn’t willing at all to go outside her comfort zone. Sadly, she got given the choice you’ve already faced.
So in summary, read up not just about your work, but about anything vaguely related, and most of all, don’t be afraid to say “I’m not quite familiar with that work / concept, however…., because….” Then relate that back to your own thesis in some way.
And yes, know what your examiners have done in the past – they will expect you to. It also helps that you know where their expertise really is….