This won't work unfortunately. By buying a MIDI-USB converter all you are doing is adding MIDI in/out functionality to a PC that doesn't have it already. You would obviously be able to transfer MIDI data between the KN6000 and PC as required, but there is no way that you could use MIDI to remotely access an SD card from the KN6000 as there is nothing in the MIDI protocol to enable this, and you have Windows sitting in the way on the PC too.

Richard.