Tim, it would not be a bad idea to get a Pa500 and a Psr s900. I have a 500 and I can't hear the difference from the 800's demos. The DNC sounds have not been very impressive for me at least from what's been shown in the demos so far. People in the forum say the 800 has a better sound definition but you will probably notice that if you have a 800 and 500 side by side. If you are an amateur the 500 will be more than enough for you, however you'll miss the good keybed, aftertouch and the use of the EC5 pedal. You can check in my video how the 500 sounds in this orchestra setting. Only the lower manual sounds and the middle manual oboe are not from the Pa500:
http://www.youtube.com/watch?v=8vClD9eMq10

Good luck

Victor