Hi,
I have been to same case where on first time load i had to display all data by default, so what i did was i took "ALL" as first value in all of my combo box's and made it as by default selection label 1, then on excel i applied formula if value in that cell become's all then it should go blank.
for example:- suppose my destination cell of combo box is A1, then i applied formula on A1 cell "=if(A1="ALL","",A1)".
i Hope this will help you.
Regards
Rahul Sharma