Currently XCubes for Windows allows the use of external datasources to import data by using a link mechanism. The sources are SQL databases, MS Excel files or MS Access datasources. The Links are not currently available in the iOS version to tranfer data from cube to cube.
In order to use MS Excel files and MS Access databases as datasources you might need to install the Microsoft AccessDataBaseEngine component. It can be downloaded at the following address either for 32 or 64 bits systems. https://www.microsoft.com/en-US/download/details.aspx?id=13255