#3, same concept as #2, with the F in negative space cut from the 6, but this one has subtle dimension with the orange highlights giving the F depth. A bit of a trompe l'oeil, which also plays up the sixth sense idea.
We like the new direction here, new colours (maybe tweak) and your ideas. The F/6 icon is possibly too clever. Like the notion that it is clever and reveals new layers as you ponder it, but it needs to draw you in a bit more.