Nice joro... look forward to the next version - with mics...!
FTG - I've done a lot of stuff with open tunings over the years but not so much in the current work - more my instrumental work.. what you're hearing as "that amazing sound" is three things:
(a) double tracking, as joro's mentioned - I always always always double track acoustic guitars - it fills out the sound and covers a multitude of recording sins at the same time... win... now joro's started playing different things on the two different tracks then brought them together and played the same thing so you have this chorusy effect caused by the minor variations
(b) the "drone" effect of open tuning. Your standard Spanish EADGBE tuning isn't really a useful chord on its own. Joro's using CGCFCE which is sort of a C major chord with a 2nd (E) thrown in - strum straight across that without any
fingers on any frets and what you get is this sort of slightly more complex major chord because of the 2nd. It sounds good. The general technique is then that you use relatively simple chord shapes - even one finger/string only - and move it up and down the fretboard to create these really strong chordal melodies as joro is doing - and because all 6 strings are tuned into this interesting chord on these own, you get a droning effect of the basic chord behind the melody stuff - in particular the C... note that there are three Cs in the 6 strings...
(c) the lower pitch. Joro's E string is 4 semitones lower, at C, than a normal E, his A string is 2 semitones lower at G, than a normal A... etc. so you're getting this different, lower sound as well that you don't normally hear with acoustic guitar
That combination is what's getting you in... I love it - it does have its limitations but then you can always retune it some other way to get a different sound...