The KN7000 SD Card system is only capable of addressing up to 1 Gigabyte. Unless you intend to save hundreds of MIDI or MP3 files, I would guess that the average user would really have no need for even a 1GB card

For example : Assuming that a typical KN7000 sequenced file, or 'Performance Save' requires about 50KB of storage space, then if you fill the SD Card completely (20 files per Folder and 99 Folders) then the required storage space is : 50KB x 20 x 99 = 99MBytes - well within the capacity of even a 128Mb card
Of course, if you opt to save additional components, on Page 2 of the save dialog, then the required space will be greater, but still well within the storage space, of the 'lower' capacity SD Cards.