As of Jun 2018 here are a couple links that work.
What I Thought I Knew about Spiritual Death
The whole series is at Understanding the Fall
There is not an easy way to find the series on their site as of Apr 2014. Following are the articles.
A. The Path of Sin
B. The Path of Adam's Fall
C. Spiritual Death
5. Spiritual Death Quiz (The software that kept score is broken, but you can definitely still take the quiz)
8. The Fall of Adam and the Fall of Me (this one was a draft; I hadn't finished the conclusion yet)