Scott,
The PM PrepCast is not an "audio version" of the PMBOK Guide. However, the PrepCast is a PMP exam prep that follows the PMBOK Guide closely. We are not allowed to simply "read" the PMBOK Guide to you because PMI owns the copyright.
What you will see however, is that our episodes 04.xx - 12.xx are pretty much following both structure and content of the PMBOK Guide.
So for instance if you are reading chapter 5.5 in the PMBOK Guide, then our lesson E05.05 covers that material. Again... not a 100% copy but as close as we "dare".