Nice! A couple of questions:
1. Why transform the bounding frustrum into lights view space?
2. What is the point of the crop matrix? Couldn't the 'scale' go into making the ortho matrix? What is the purpose of the 'offset' - to translate the view matrix from the center?
Short answer: you need the min/max values by the light point of view.
Here you can find the answers, this is a nice nvidia paper. It was a great reference for me, at least. The algorithm is described on the 7th page.
Another good reference for PSSM.