The KN2600 has the SD Card which is like getting a hard drive(s). Strangely the 2600 has no floppy drive like it's Papa, the 7000.
The KN2400 does not have the SD Card, but rather only a floppy drive.
It is my understanding that both are compatible with the 7000, so I would asume, like the KN7000, the KN2600 and the KN2400 will be compatable with all KN Keyboards, although I'm not 100% sure of that.
Tough Decisions picking a keyboard now-a-days. They are all really good.
Larry "Hawk" Hawk Music
♫ 🎹🎹 ♫ SX-900