Yes, I played the PA3X for two years plus, and now have a PA900.
There are a lot of similarities and also differences.
The 3x has more programmable controllers. It has a more extensive vocal harmonizer and processor, although the one in the 900 is good too.
It has the MAXX sound processing for the overall e.q. and sound parameters.
The key feel is supposed to be the same, but I personally think the 900 has a little lighter and faster action.
900 has a bigger screen. Both have touch screens.
The 3x has more styles and sounds, but they can be used in the 900.
I didn't compare them side by side, but the sounds is similar, not exact.
If you have any specific questions I'll try to answer them.
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DonM