Comparing values between 2 matrices (matrix)

Hello
I have two matrices. One contains sales data for the current year, the other prior year. Both matrices use different data sets

I'd like to compare the two - possibly by creating a third matrix that subtracts prior year from current year.

Any ideas? When I create a third matrix and substitute a formula like =sum(values, "Data source for matrix 1") - sum(values, "Data source for matrix 2"), the resultant matrix subtracts the grand total from the first matrix - not the individual "cell".

Any suggestions are appreciated.
Thanks

I would like to know the official answer to this too...

see http://forums.microsoft.com/MSDN/ShowPost.aspx?PostID=1673719&SiteID=1 for simular question...