Nspace

I have found enough time to patch 78.07. Sorry for the long wait.
This is patched firmware version 278.07, based on factory firmware version 78.07 for the Axpert Max E 11 kW Twin '28066. Do not use with any other model, not even an Axpert Max E 11 kW Twin with '2809 DSP (it will refuse to update the firmware).
This patch implements Georg594's patches for firmware version 90.06, but applied to 78.07. It also fixes the premature float bug, and changes the version number reported by monitoring software to 278.07. The display will still show 78.07. The current threshold is changed from 0.50 A to 0.05 A, and the minimum MPPT voltage is changed to 200 V.
Use at your own risk; I do not have a Max to test this firmware on.
Firmware upload instructions for models with a removable display.
dsp_278.07 patched 200V.zip

It won't update, just as your mismatched 8 kW didn't update.
It's sad that some resellers don't know about the different DSPs.
However, the difference between '28066 and '2809 firmware is just one start-up call to a function in ROM (Read Only Memory, different from Flash memory). So I might be able to modify this '2809 firmware to become '28066 firmware, then package it up with a different reflash tool and it should work. I did that once before; I can't recall if I got any feedback on whether it worked or not. I need to do some checking.

Bought my 3.2 volt 100 Ahr cells from a company called Cinch-IT in the Cape. New cells, not 2nd life. Bought the BMS on a special from BidorBuy
Also bought some 2nd life 50 Ahr cells from Electromann in JHB as I had a spare BMS. Looked a bit dodgy at first but currently working fine.
Used aluminium flat bar for the links.