Diki"s comparison says that the Grand Piano Sound on the PA800 is much better but Korg has made this piano free of charge on their website for loading into the PA1X and they have also given you free of charge the extra styles not found in the PA1X but in the PA800.
The keys on the PA1X are semi weighted and therefore feel much different than the light keys of the PA800. Both keyboards take the same time to load a set of new samples the first time you load, but the PA800 auto loads a faster. The PA1X has 8 faders to use to adjust volumes, effects, drawbars, etc., the PA800 only has 2. There are more outputs on the PA1X. The PA1X is heavier but in my opinion has a better build quality.
Now, I have one PA1X still at my store (these have been discontinued) and it has a hard drive installed and an optional grand piano board (different than the pianos in the stock machine and the PA800). Oh, that's another difference. You can have two expansion cards installed in the PA1X and none in the PA800).
My price is a lot less than you have posted above. Please contact me if you are interested in a great price for the PA1X or a new PA800.
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George Kaye
Kaye's Music Scene
Reseda, California
818-881-5566
www.kayesmusicscene.com