HP Z6 G4 inaccessible boot device

[OS-Cubed]

I have an HP Z6 G4 that has been running fine for years now, including all updates to windows 11 24h2.  Recently I installed an update to the BIOS to 2.96.  After updating my system no longer boots properly. I get an inaccessible boot drive error that is consistent with a mismatched ME and BIOS - and the 2.96 bios does not allow a downgrade back to a working bios.  I have completely tested and restored from scratch from before the update the hard disk so I know it's not that.

So, no problem I'll update the Firmware for the ME. Nope.  I tried under a usb booted into the windows PE environment and get a "side-by-side" error that indicates that there are no c++ runtime in the PE environment.  I tried a bootable USB Tianocore EFI shell and the fwupdlcl.efi command with the latest ME firmware and get a "error 8714: firmware not updated due to file open or read error".  

When I try to open a case with my serial number and the model number it claims my model (815262WR-999) is invalid (That's literally what it says on the bios screen), along with the serial number, so I can't proceed on to the next step (why HP needs both is beyond me - it accepts the serial number).  Bios says P60 2.96, ME firmware says 11.22.97.2675.  Firmware I'm trying to update to is 11.22.98.2728 which was the latest version indicated in the drivers section.

My machine has now been down for a good long time as I was trying various restore methods thinking this was a hard disk corruption or something.  I'm stuck on any next step at this point (for reference I've been selling, servicing and supporting HP machines and Compaq machines since their inception.  I have TONS of debugging and troubleshooting experience (hell just getting an EFI boot disk set up was a bit of a challenge here but it worked fine except for actually running the firmware update.

Any other ideas?  I know this is an old machine but it's been stable AF for ages, until now.

[OS-Cubed]

Alternatively how do I raise a case on my machine, since it takes the serial number but not the model number.