I'll install the old CPUs and keep my fingers crossed so it POSTs. Was there a key combo that allowed you to flash a BIOS from an USB in recovery mode ?
EDIT: System is dead, only the chassis fault light blinks, tried to load the BIOS as SUPER.ROM on a bootable USB and hitting CTRL + HOME like...
Unfortunately the board won't post after downgrading to this BIOS version, probably because it's is too old to support the CPU (2 x Xeon E5-2670v2), IIRC this board had older CPUs and when I upgraded it with these 2670v2 I had to flash a newer version before the board could post.
XD9Ai with BIOS 3.3 Here! , I'm stuck at the ACPI_BIOS_ERROR, did the BIOS reflash with JPME2 set to position 2-3, still no luck same error (no ethernet cable connected, sleep set to S1).
Any chance that OP has kept a copy of BIOS 1.0b which seems to allow Windows to install ?