Dave,
That was fun to read!
About the difference between the S80 and P80, there are many.
First, the P80 is using a chip from the Clavinova products and the S80 is using a chip from the Pro EX5 keyboard but with many new acoustic sounds. The biggest difference in the Piano sounds would be that the S80 using 4 different pianos including a Yamaha S-700 concert grand sample set from a $250,000.00 custom made grand. Also, there is aftertouch and other pro midi controller options which is not on the P80. However, the size and weight of the P80 is great. Both are priced really great for their performance and sound features.
George Kaye