I only use my cards for saving settings etc. and the odd downloads of member players and I find the KN SD-Explorer is easier and quicker for this purpose than anything Technics can offer, besides which. all I seem to get from Jukebox is that irritating Demo tune so I don't bother with it.
However, I would have thought some form of PC/KN contact would be needed and I may be wrong, but isn't that what the 'convert' section of Jukebox is for. Do your audio files need converting to another format perhaps? What made me think of that is quite a few of the song's that Bebop sends to me, Windows Media Player cannot play because it doesn't recognise the format.
I am very interested in your problem and hopefully, you will get an answer from one of the many member experts. I will keep on visiting this site to see what happens.