Is my only option to use SD card and this guide to get the FW that has a 'drop down menu' to Overclock...eg +1.5th, +2Th etc??
Yes, unfortunately, your only way out of that firmware is through an SDcard recovery, you can use T9 recovery firmware on S9, download it from >
https://service.bitmain.com/support/download?product=Flashing%20SD%20card%20with%20imageAnother question would it allow me to upgrade to latest BRAINS OS? without messing about as above??
Obviously NO!.