Two different boards that's why.
Each board has certain differences(chipset, other functions, cpu type,
memory......).
A bios is meant for a certain board and is not common to a range of boards.
The A7N8X has differences that the X-X does not have and the same goes for
the X, and the A7N8X dlx has differences that the A7N8X-E and E dlx do not
have.
The A7N8X -E DLX has differences that the A7N8X -E does not have.
So each A7N8X board is different from each other.
If you read the specs for each board you will see the differences anyway.
And if you take the time to read what it says regarding what exact board the
bios is for you will see that it cannot be used for any other.
Always get the bios from the motherboard site and not from any other source.
Always read what is says about the bios and for what board.
No need to upgrade/update bios unless you are having the problems that are
supposed to be fixed in a bios update.
If it aint broke dont fix it.