No, i genuinely don't have anything else to try sorry. I don't give up easily but have to say, somewhat cynically, this: The way the fenix firmware works seems it may have been intentionally designed to defeat any conventional recovery methods. I'm sure that's not the case but from a practical viewpoint that's how it plays out.

Maybe if you can track down the author/s of those hidrive modified fw files you might get some further insight.