Awesome! Thank you for the upload.

I've been able to confirm that you can't re-image an X10 to a Giant B by simply pushing the STM firmware down and using the Giant B image for the Pi Zero. The structure of the firmware is very similar to the X10, but it looks like the algorithms are hard-coded into the firmware. I was hoping the firmware was just acting as a USB to SPI translator, but it looks like it's doing more low-level work for the algorithms and to drive the chips.

I've also been able to get a successful decompile using Binary Ninja and the Thumb2-linux architecture, but this will only get you machine code afaik.

Edit: Here's an upload of the GB and GX10 firmwares and binary ninja decompile databases: https://ufile.io/ues7g
If someone knows how to diff two SQLlite databases, that would be helpful.