tldr: wondered if the small and equally big file sizes of some transferred recordings seemed legit, to get a hint if the files were corrupted. But it was possible to check it directly via the keyboard's additionally added usb interface, so nemas problemas.
Ok I should maybe describe it a bit clearer just in case: wanted to see if any of my backup files were intact, and I discovered it was possible to play back the .usr files directly from the usb-stick - which had been inserted into the keyboard - without having to wipe/substitute the current recorded tracks by importing/loading the .usr files first
