Quoting the OP:

"However, when I plug in all the textures to the PhysicalSurface node then everything behind the plane gets tinted the colour that is mapped to the plane EVEN if the transparency map shows full transparency for parts of that plane."

Hard to see what is going on without seeing a screen cap of your node connections. Just a guess .... You wouldn't have "Colored Transparency" checked by any chance, would you? That could cause that behavior. If you do have it checked, uncheck it.