Texture splatting alpha channel question.

I have a game that I'm trying to port to unity from an older 3d engine. The game makes use of texture splatting, and uses 5 layers per chunk (4 texture layers and 1 shadowmap layer). Each layer uses a source texture that has a normal and a specular version. The alpha layer of each texture contains a black and white inverted copy of the texture.

What is the best way in unity to recreate this? Should I create new textures? Is there a shader in unity that takes the specular per vertex and multiplies it by the alpha of the layer texture?

The reason I'm asking is that the imported textures are extremely shiny in Unity, They don't reproduce the subtle shimmer as the other engine does.