I started constructing this puzzle as a monthly midi contest entry (from a while back!), got stuck in one section, ran out of time, and then left it in the constructor. Here, I have taken it out of the deep freeze and reheated in the microwave for your consumption - no doubt magma-hot on the outside whilst still frozen on the inside.
I present it here as themeless - but those of keen memory might spot a central theme idea :-)