@der][meister RE:6900XT I just stumbled on morepowertools RED BIOS EDITOR and MorePowerTool for Polaris, Navi and Big Navi – MPT 1.3.7 Final (New)
Just getting reading now..

https://www.igorslab.de/en/red-bios-editor-and-morepowertool-adjust-and-optimize-your-vbios-and-even-more-stable-overclocking-navi-unlimited/ If interested.
Now, I know there is some life after RX580 bios / modding on Navi /Big Navi cards.. This seems like this tool mods the powertables (in memory) as opposed to flashing the BIOS I maybe wrong tho.. will see.. Research continues.. 

Note, I have Samsung GDDR6 Memory So ,this is great news, idk if these cards come in any other flavour memory chips like my old 580's Hynix/Micron/Elphidia/Samsung..

Now to get these thing running on PhoenixMiner.