Graphing/tabulating a multi-sheet/workbook formula with single variable input

I have 2 long convoluted workbooks that have hundreds of inputs resulting in a net cost and margin for 5 products.

I want to chart how a some variables affect both these values (cost and margin) for the 5 products whilst I change a single cell (discount %).

I've tried to get through the what-if tabulation function but it requires the formula in a single cell, which isn't possible.

What would people suggest to produce a table (and therefore a graph) that achieves what I need?

I can manually change the cell and copy the 10 results on to another table, but this is long winded and I believe Excel can help me here - but I can't see how yet.