Sorry for raking up such an old thread. I'm on 9.1.8 and I've been investigating this. For some reason, all the 'default' guitar tunings in the Score Settings are 'wrong'. They're all one octave higher than concert pitch. The bass ones too.
I'm really clueless about this. Ideally, the MIDI tunings should be set to concert pitch (i.e. the lowest string in standard guitar tuning is E1, not E2) and a transposing stave in staff notation should be used while the tablature should play E1 for an open E string note, i.e. be non-transposing. But the way this works, the tablature sends MIDI notes that are one octave higher than what is expected according to the display. Am I missing something or is this actually some kind of oversight on Apple's part?