Sooo this question is a problem , a evolution by another solution of this problem here:
We have a "Eye" (HTC Vive). We have a "Parent" which is the Parent of "Eye".
We can not change the position or rotation of the Eye in code. We can only change the position and rotation of the Parent.
1.We want to modify the Parent Position so that Eye to goes to a certain "Target 1" position.
2.We want to modify the Parent Y-Rotation so that the Eye looks at a certain "Target 2" position.
3.While doing this we dont want to modify the Parent X or Z , because this would lead to a Rotated game experience.
The Parent Position changes so the Eye gets to "Target 1" position. The Parent Position changes so Y- Rotation should look at Target 2 position The Parent X/Z Rotation should not modify the Eye X/Z