@EmilEmilchen firstly, welcome to the community.
We have a few threads on these boards around the forum. I actually starting learning on a DX79SR 8 years ago for the same reason! Unfortunately, to the best of my knowledge, no one succeeded in this quest for the reasons you already mentioned.
It’s more than just microcode, or even microcode + ME replacement. There are modules in the bios which would need replaced too. And given the semi-proprietary nature of Intel’s UEFI from this era I don’t think we ever will succeed.
You can read more about our efforts at this link: Dumped Bios DX79SR - Question regarding Ivy Bridge - #26 by IntelModder
I think there are also a few other threads too.