Hi bpsafran,
Memorizing Song paths to the Panel SONG I - IV buttons is described on page 28 in the Tyros5 Owner's Manual. (Also see the attached screenshot.)
In the Song Selection display, you have to press "View" (upper "7" button) to call the List View display. Then select the desired MIDI file, press "Memory" ("E" button) and press the desired SONG button. Finally press Exit to leave the Song Selection display and test if the button calls up the correct drive and folder now.
If desired, you can of course switch the Song Selection display back to the Icon View by pressing "View" again.
Hope this helps!
Best regards,
Chris