Thanks for being so active on this!
Unfortunately, yet again, no dice.
The GPU still appears with "No Kext Loaded".
In the meantime, I've managed to install Windows and the proper drivers so I'll be toying around with that over the coming days.
I've done some more research as well and it turns out that there's currently no tool capable of extracting the VBIOS from the XTXH variants. As far as I can tell, a tool exists, but is not publicly available thus far.
The only XTXH VBIOS I've seen in the wild has been a leaked one.
As such I think it'll take a few weeks until the right people get their hands on these new cards to properly develop, test and actually release these tools. Until then, there's little a layman like me can do, unfortunately.
I think the best medicine here may be time.