So the reason I pointed you to that existing discussion is that you asked if it were possible to share textures between Starling and Away3D.
(not necessarily whether booster's sample code is directly related to what you want)
That thread documents that you need to be at least sharing the context. So make sure you are doing that at least.
Then flexwiz said:
I actually managed to use a Starling texture in the 3D scene when using sharedContext.
However, this is a bit of pain, since you need to extract the base texture and pass it to an away3d 'texture2d'.
And as expected, the part of a Starling or Away3D texture or sprite sheet that is actually on the graphics card (and that would be shared) is the underlying flash.display3D.textures.TextureBase instance. Whether the Starling or Away3D wrapper class made it first or not is irrelevant, this is what is shared.
In Starling it is fairly simple to get at an existing flash.display3D.textures.TextureBase.
For an existing Starling texture it is just texture.base().
If you just had a flash.display3D.textures.TextureBase and wanted to create a Starling wrapper texture for it, that would just be:
new ConcreteTexture(base:TextureBase, ...)
Now when it comes to Away3D, I am not familiar with the proper official way to create an approprite Away3D texture given an existing flash.display3D.textures.TextureBase. That is what you need in order, for example, to create a TextureAtlas in Starling, and then be able to reuse the same atlas.texture().base() with something in Away3D.
flexwiz seems to have accomplished this from what I interpreted from their quote.
Just quickly checking the sources of Away3D, maybe you have to subclass away3d.textures.Texture2DBase and override the createTexture(context:Context3D) and uploadContent(texture:TextureBase) where your subclass called something like 'StarlingSourcedTexture' is constructed from an existing flash.display3D.textures.TextureBase and a reference to its Context3D and you do the appropriate checks to make sure createTexture() returns this existing instance if it is for the appropriate Context3D.
That is all off-the-cuff, maybe someone already using both Starling and Away3D can suggest a more straightforward way of getting an Away3D texture setup from an existing flash.display3D.textures.TextureBase.
EDIT: Maybe it could also be easier to create the textures and spritesheets within Away3D first, and then using getTextureForStage3D(stage3DProxy:Stage3DProxy):TextureBase you might have an easier time making the Starling versions using the ConcreteTexture constructor. At the end of the day it shouldn't make a difference whether Starling or Away3D made the TextureBase first...