Hi,
You need to look carefully - 4 SRM at 8 degrees plato indicates the extract dissolved in water. 8 degrees plato OG in a 5 gal batch is equivalent to an OG of 1.032 which is about 4.5 lbs of malt in 5 gal of water. So that would put the Briess malt at about 6 SRM to achieve the numbers you quote.
So if you want to enter the Briess extract in - it would go in at about 6 SRM color to get the numbers Briess is quoting.
Brad