ketron has told that os5.0 is the same of os4.2c plus some protecion introduced for uk pendrive. as I remember os4.2c was done many month ago (only for beta tester) and the guitar mode was on it many month ago. you can see it in the first decribe of amsonic 1 year ago (then was ketron news, not aj) ahah.
probably when the prepare out the 5.0 forget about it and think that this os has only bugfix and nothing new, then they forgot to mention the guitar mode and then create new pdf manual
that is only what I'm thinking maybe is different.
mistery is how use it