And it ain't a fraction of the size of some of the GIGA pianos, or Ivory...

ROM piano in the G70 is 64MB uncompressed... You want good quality four way pianos, it takes at least that, IMO. Just got the KSounds Vol2 piano for our K2500's http://ksounds.com/html/volume_2.html (check out the demos ) and it takes about 16MB per layer. BTW, you can get this in Triton format (as well as some others), so perhaps it is compatible with the PA2X?
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An arranger is just a tool. What matters is what you build with it..!