That's what render # 13 there shows- it's working. There is light passing through just the transparent parts of the cube that is positioned between the lights and the ground. You can see that right? The cube has the trans map in post #4 applied, all I did was increase the contrast a little. I wish it was crisper but that probably is a function of the light start and end settings or some esoteric thing like that...

"Your work is to keep cranking the flywheel that turns the gears that spin the belt in the engine of belief that keeps you and your desk in midair."

Annie Dillard