-MIDI transfers can be tricky, since the MIDI technology is over 30 years old! Modern computers are actually too fast for the MIDI system to keep up with. There should be a buffer control/delay setting on Kfuenf's settings that you can increase to help the K5 deal with the data being thrown at it. This seemed to help a little, but was not a complete fix for me.
-In Kfuenf, I could not get bank sets to load at all. It would fail every time! I had to resort to loading individual single and multi presets, one-at-a-time.
-It usually took several tries to get the transfer to work for each preset.
-As an older technology test, I also tried transferring K5 presets back and forth to my Ensoniq ASR-10's floppy disk drive, which can specifically save MIDI System Exclusive data files. But this gave me the same kinds of results, where it took several tries to get the data to transfer
I hope someone out there has a better solution for you. I gradually was able to audition all 10 banks of single and multi Kawai presets, but it was a tedious process. When it was all over, I picked my favorite 48 single presets and loaded them into the K5 for good.