by "loopable" i meant if if will continue to four or if after the last value in the array it will "loop" back to the first. So if we add always (++) it would "loop" through the values inside the array.
But i made a couple of experiments and it seems it's not like that.
Well, anyway, i have good news!!!
I think now EVERYTHING is working! 8)
Surely it is not the most elegant nor the most genial code, but hey, it is getting the job done!
This will be the V1.0 of (maybe) several to come... 
Now the piezos are working, the buttons and the pots also and the button is also enabling us to choose from Ionian (major), Aeolian (minor) and Major Pentatonic Modes.
Now it is time to try to plug it to some music software and get some sound from it!!!
Also time to start thinking about building a nice "real music instrument" (maybe out of wood).
== = = = == === ==== == = = =
i have still one more question that just came to my mind.
i thought a couple of times that it could be useful to have a little led somewhere blinking whenever there is some "communication", like the TX led in the Arduino Board.
How could i do this?
I noticed that there is a pin in the board (digital pin 1) where it also reads TX. Could i use it?
Thank you!
=)