Your RAID controller is?
Intel RS2BL080 or similar?
If so, just use a DOS bootable USB flash drive created with RUFUS or similar: https://rufus.akeo.ie/
That way, the EFI requirement doesn't matter.
Provided it's an LSI / Avago / Intel based RAID controller, you could also flash it in Linux or Windows, there are many options.
In order to provide you with a resolution on your case, we would like to know the following details:
*Intel RAID Controller model used on your integration.
*The link of the update package you are trying to apply to the RAID controller.
It is correct. The Intel Server Board S5000PSL offers EFI version 1.1
Some of our Intel RAID controllers offer more than one way to install the firmware on the controller. Feel free to share the model of your RAID controller to further investigate this for a resolution.
We would like to follow up on this matter and see if you were able to update the firmware of your raid controller. By any chance do you have the model as previously requested?