invisibleman18:It said the code was invalid, but did work when I went as far as checkout through the normal store to compare pricing. So I figure you can't use that as well as the EPP discount. So I guess the $100 was either due to the payment method or the particular EPP group.
Just to resolve this I've just been back through as far as checkout to check and the extra $100 off was for using Q card. It takes $100 off if you select laybuy or Q card.