Thanks a lot for posting. It took me a while to figure things out too and your comments were very helpful. I didn't realize at first that there is an Appendix list of sounds that came with the PX-560 (it is also downloadable on the Casio support website). With that list and the MSB and program numbers, you can choose any of the sounds. And with the ease of saving setups and naming them, iMIDIPatchbay is great for quick performance changes.
On a side note, when I first started the app, I got a message saying it would not support the next iOS. I was concerned because I also read this online somewhere in another forum, so I contacted them and was told they will update the app before iOS 11 comes out. If that holds true, then this is also great news.