You are right. The Voyager has three voices or oscillators. The second and third oscillator are tunable in relationship to the first oscillator and each other. In addition, the Voyager has a fine tune knob that can tune the whole keyboard up and down by maybe half a tone or so. In synth and techno and other related genres, players use all of this capability to really create some interesting sounds. In pop and rock and other related genres, I think digital keyboards as a whole are tuned up or down to thicken the sound or add a tonality that you can’t put your finger on, but in which you know something different is going on.
I was just playing with the fine tuning on my Hammond XK-3c. I can tune the whole organ from 430 to 450. As I play music and tune up, I hear something going on and some dissonance. But within 2 seconds, the raised tuning (even at 450) blends right in with the music but offers something different.
It sounds really weird to be playing at 430 with all sounding well (because your ear has accepted or adjusted to the tuning), and then while playing to music, raising the tuning up to 450. While you are raising the tuning, you can clearly hear strangeness. But again, within 2 seconds after reaching 450, all seems well. Yet the sound could be considered thicker or “whatever.” It is different, but not unpleasant at all.
I will address your other questions in a minute.