I tried to update the latest bios on my X8DTN+ motherboard and received the message saying "bios is write protected." According to the phone support, my motherboard is an OEM board with UEFI BIOS provided by Intel. Intel support is claiming that they cannot provide BIOS updates as it is not an Intel branded board. Would you be able to find out which OEM I would need to contact in order to flash my bios to the legacy AMI bios?
You need to contact Intel Platform Support for the BIOS update and they provide the UEFI BIOS only. You can't use the regular BIOS from Supermicro website, unless you program the BIOS using the hardware programmer. There should be a note & a CD came with your motherboard, that explain where to obtain the UEFI BIOS update.