Hi Andy.
I have a Mac myself and maybe I can help you with the RS232-DB9 cable. For a while I was looking for one and finally found one which worked with Mac. In the end I didn't need it and sold it here a while ago.
It was a USB to Serial adapter (Brand, Keyspan). They are a bit pricey but it did work on my machine. Then you will need another adapter on the other end.
http://www.ebay.com.au/itm/Keyspan-U...5e3ef87&_uhb=1