Can I use Roland guitar synthesizers and divided pickups with flat-wound guitar strings?

Are the GK-2, GK-2A, and GK-3 pickups compatible with all GR-series guitar synthesizers equipped with a 13-pin GK pickup connector?

I usually use the Select switch on the GK controller to switch between the GK pickup's output and the regular electric guitar's output. Is there a way to switch pickups using the pedals of the GR-20 unit?

Roland makes many products with the 13-pin GK connector. Which of these products are not compatible with the GK-2B Divided Pickup?