It's an easy thing to check, though.
Thing is, if the mike pre in the PA900 is killing the sound, doing all the work BEFORE you hit the inputs is probably the best way to get what you want.
But if the issue is with the entire signal chain in there (maybe the A/D converters) then the pre won't help a lot.
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An arranger is just a tool. What matters is what you build with it..!