I would like to have a null moving/sliding a 2 layer GFX on the x <--> but each of the layers need to "seem" as if in a bit of a different depth.
here is a great example of the look: http://space.vanderlanth.io/ - The 2 layers here are images/ text
the side sliding...
To get started you can do this. Create a null. right click position->Separate dimensions. Animate the x. Then on the layers you separate dimensions also. Alt-click x position of the layer and pickwhip to the x of the null. Same for the second layer, but you just add something like *1.5 at the end of the expression. This layer will move 1.5 times more/faster.