I am not using nGui but I downloaded your sample. I studied it 10 minutes and know I understand. You take from the sorted score each score and you find in what index is in the unsorted scores. At the index you got, that index is the username for the score.
I'm not very sure of myself that I can make it work, but I'll try right now and let you know if I got something.
EDIT: WORKING!! Thank you very much! Now I'm working on a "save-data", so everytime someone loads the highscores, the same values remains until someone get a better score. I may let you know if I get stuck somewhere, but your help was extremely usefull. I upload a photo from my Highscores to let you see how it looks.