Do not dived object to elements! Assign different materials/maps to needed faces and:
assign Mesh Select modifier to mesh, then in this modifier in face-level choose every faces with the same material and uvw mapping. Keeping faces selected assign to'em UVW map modifier or UVW unwrap. After that you can assign Mesh Select to another group of faces and then apply to them another UVW mapping. And so on many-many times. It dosent matter how many modifiers you have in modifier stack. Good Luck.
