I just bought the CD's about two weeks ago, and I bought the PRing course over two years ago --- so the CD's weren't even developed at that time.
The CD's I actually like better because they break down all of the sections into "tracks" on the CD. It is easier to maneuver your way through the CD than on the cassettes!
The sound quality is very good.
You will notice one difference between the tapes and the CD's. The second book in the PR Whole Mind System that I bought (tapes only) has 'Learning to Learn' by D. Trinidad Hunt. The second book that you PR in the system on the CD's is 'Natural Brilliance' by Paul Scheele.
I still like CD's better, because if I have sections I really like to go over, it is easier to find and replay.