The manual says "If the MODE is set to KEY SPLIT, then this key is specified here. Any note above or including this note will play the upper manual, any note below this one will play the lower manual."
I don't get this to work. Any values I give the Key Split (e.g. C2) have no effect. The Mode button on the Organ is set to Key Split. If I change it to Lower, the whole keyboard has the Lower sound, and if set to Upper, the whole keyboard has the Upper sound.