Thanks Guys
In fact I have tried both pa3x and pa900
All the voices of the pa3x are in the the pa900, and you can add some more voices .
The pa3x has a section of effects that is not present in pa900.
And sliders not present too. With the Pa3x you can create samples. The Pa900 can load samples but cannot create samples.
Ther is one thing the pa900 can do and the Pa3x cannot : load soundfonts samples !

Sure there are somme differences to justify almost the double in price.
The better is to go and listen carefully and try the pa3x and pa900.

With the same budget I bought the
pa900 and the 88 keys yamaha MoXF8

I hear that tHe pa4x might be announced (namm 2014 ?)