So I googled this:
"what are the extra straps with the OZ tower for?"

And found this:
http://www.boatcoversdirect.com/prod...wer-bimini-top

If I understand it correctly - without having ever seen any of this - it sounds like the straps are intended to secure the various arms of the bimini to each other when the top is deployed. Presumably to stop rattling or wobbling or to enhance wind resistance?

Just a guess.
If I am right I am giong to want a pull if I ever make it to Australia