@Tabashir: thanks for your helpful tips.
I have *finally* - after about a year of trying - managed to update the firmware. I could not get the CD to work even as you described. But by removing all the other USB devices, I was successfully able to get the USB stick to work. Hurrah!
But what a complete pain this has been. Sandisk = this is an object lesson as to how to frustrate and annoy your customers. The testing on your Sandisk Toolkit is inadequate (did you actually try burning a CD using it??? Where is the download stored?) And the instructions and help for Mac users is inadequate.
It does not make me feel inclined to buy another Sandisk SSD to be honest.
