AJ is the U.S. Ketron distributor and an engineer who worked with Ketron in developing many of the Ketron features - he knows Ketron.
I had the floppy drive replaced with a USB drive a couple of years ago, and it was limited to less the one gig. The new USB drive allows for at least 32GB for the USB drive and about the same for the card drive. It can also play MP3's and WAV files.
When I got the SD1Plus back, it was like a new instrument, meaning that it was empty, so, back to creating and saving registrations, and the hundreds of midi files that I have saved on the PC ALL were edited on the Midjay Plus. I have to re-edit them - again - on the SD1Plus. For now, I'm using the SD1+ as a controller for the Midjay Plus. The Midjay Plus is my 'go to' arranger as I also use it with midi accordion and more frequently with midi files and a keytar. I'd check with both AJ, and on your side of the ocean, you have Tonewheeldude. Good luck.