Dennis, thanks for that excellent explanation of how you're able to link and call up a songbook file on your Pa2 from your iPad via midi control change messages. That's real cool.
Unfortunately, I don't believe it's possible to do the same with the iPad & the Yamaha Tyros 4 as I couldn't find anywhere in the Tyros 4 Data List Manual (midi implementation section) to show either 'Registration' files or 'MusicFinder records' supported or recognized via midi control change or sysex.