Hi dogman

George and Fran and others may say differently, but I would consider the KF-90 and the GEM SK880 to be very different instruments. Of course, they are both 88-key arrangers with vocal harmony. However, the GEM SK880 has sliders, wheels and aftertouch, sample playback, styles with audio loops (RASS), and mass storage for 1000s of styles. The KF-90 has a more modern sound engine and probably sounds better. I consider the GEM SK880 to be a slightly outdated high-end arranger, while the KF-90 is a digital piano with arranger features. hth