Crosstab with multiple rowset xml content

I have multiple rowsets (xml files) which I want to calculate subtotals from. Each xml data set has identical columns. If I union all the files together, the xml content contains multiple rowsets and the Crosstab function does not give me a summed value of each column, but instead it creates a column for each column in each rowset.

The Normalize and the rowset combiner transform both combine rowsets by appending the second dataset into new columns, is there any way to append the data into new rows instead?

Because my final file is going to have something over 30,000 rows (14Mb), I am reluctant to use a repeater on each row of each file to combine it into a new rowset. Is there an efficient way to handle this calculation?