The rumors of an impending PA900 are out there... You might want to hang tough and wait. The five fill system (as opposed to the old 3 fill system) is a paradigm changer for Korg. Plus the Chord Sequencer...

Me, if I was even considering a PA800 and the PA600 wouldn't work, I'd wait...
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An arranger is just a tool. What matters is what you build with it..!