I'm ready to start hacking my 109 --
Do I need to convert my 109 to an A09XL (viaDVRupdate.exe) before I install the Buffalo v8.40 ?
Or will the Buffalo updater alone do everything?
You don't need the A09 FW and you don't need the Buffalo Updater just what is inside the updater (kernel + FW). Check the Buffalo 8.40 thread for instructions using DVRUpdate (though it's very simple).