Are you parsing xlsx and converting it to your format and data model? Or are you running excel instances under the hood? What will happen if there's an odbc connection inside xlsx? Will it be properly executed?
We run the Excel spreadsheets on our engine. For security purposes, some Excel features are for the moment disabled ( macros, xll, odbc ). Our take is these features are to be handled by your code, that send data to the spreadsheets. The sheet will handle the logic ( business rules, computations ) and send back the result to your app.