Kx9, I'd like to make some comments regarding Nestorianism and how we understand Christ's incarnation.
First of all, What does Nestorianism say?
Nestorianism says that Jesus has two distinct persons, a Divine person and a human person / That this union between the two persons was later broken.
This is a very narrow view of Nestorianism, one you often find in protestant circles today. Historically, Nestorianism was the belief that the Divine being of God, was united to a human being, to form one person. This belief is based on the notion that a nature is the foundation of a person, and persons are not the concrete foundation, but are rather "masks" or temporary expressions; that is, persons don't reflect the reality of things. So while Christ was formed into one person, he was "really" two natures.
Because of this, Nestorians believed that the Divine subsistence of the God did not suffer, only the human subsistence. The "person" could be said to suffer, but this was meaningless, because the person wasn't the reality behind Christ.
I'm sorry if that's confusing, but Nestorianism is a very confusing heresy.
The Orthodox position, by contrast, is that the Person is the subsistent foundation of being, upon whom nature and essence are contingent. To encounter the Person is to encounter the reality of that thing. So the Person of the Son took upon himself human nature in addition to his divine nature. The natures aren't united to create a person; rather, a Person, the Logos, unites the natures in Himself. This is because the Person of Christ, not the natures, is the foundation.
To simplify, when Nestorians say "person" they mean something like a mask. When Orthodox say "Person", they believe that the Person is the reality.
If Jesus went and preached to the Spirits in prison after his death (still retaining His Human and Divine natures in one person), does it mean that Jesus rose bodily and went to preach to the spirits in prison before He rose from the tomb bodily in a glorified body on the third day?
We believe that Jesus has a human: Body, mind, soul, spirit. He is totally human. His Divine Nature does not substitute in for a human soul or spirit. He has a human soul and a human spirit. The belief that Jesus didn't have a human spirit, but rather his Divinity substituted for it, was condemned as the heresy of Apollinarianism. Christ assumes EVERY part of humanity in order to heal it. He even assumes human Sin and Curse on the cross to heal us.
So when Christ died on the Cross and descended into Sheol, he did so as a human being. However human beings are when they die, Christ became that way--- the exception being that his body did not see corruption because he was the Messiah, sinless and with power.
If you believe that when you die, your soul or spirit goes to the realm of the dead, then that is how Christ became. If you believe that the dead have some sort of bodily existence after death, but in a shadowy form, then that is how Christ became.
I would say, however, that when Christ preached to those in Prison, he was bringing them out of Prison and into Paradise, where there is life in its undivided fullness. But that is a topic for another time.