Hi Luca, Gitools can directly open an excel file if you have your data in a "table layout" (ex: row + column + value1).
But if your data has a "matrix layout" (ex: you have one column for each sample) you have first to export as "txt" file, open the txt file with gitools, choose "Data layout is as: Matrix", click "next", change the "data layer name" and click "Finish".
If you still have problems send me an email with an example of the data that you are trying to import.
Best.