all the more reason to try R. You can just list all files and then keep only those with the relevant extensions. As it happens we have discussed several ways to import old, binary and macro-ridden Excel files over the months, so all hope is not lost but it will need some work.
If you could provide us with an example represeting your various challenges it might help.
https://hub.knime.com/mlauber71/spaces/Public/latest/kn_example_python_excel_xlsb
https://hub.knime.com/mlauber71/spaces/Public/latest/kn_example_excel_old_files_import
https://hub.knime.com/mlauber71/spaces/Public/latest/kn_example_excel_macros_xlsm