i dont think anyone is saying that the sounds on all the styles and all the individual sounds on the PA500 compared to the PA3x are the same.
I thought that was the exact reason for the original topic post.
BTW...Fran, Frans, Rikki, and Bill have it correct. Newer keyboards can play older keyboard files and will sound the same or better.
Older keyboards can (sometimes) play newer keyboard files but will not sound the same, unless the exact same voices were used, which is unlikely. Even then, the newer keyboard sound engine plays a big role in the quality of the sound that the older keyboard cannot match.