3D parametric Rectangular grid

Hi everyone,

Im pretty new to grasshopper, and Ive started this definition to make a rectangular grid for a building skin. I want to be able to play with thickness of the members, depth of the members and size of the aperture. 

Ive created a 3D grid of boxes and placed smaller offset boxes inside these to act as voids. but when I link the solid objects with and the void objects using solid difference the hole only appears in one of the boxes, Ive attached a picture of the object in rhino and the grasshopper definition, Im sure fixing it is probably a really simple solution im just not sure how to fix it. 

Or if anyone could suggest a better way of going about this where i still have parametric control over how many boxes, the sizes, the depths, and the sizes of openings. I would really appreciate it.

Thank you