The thing is, although I’m no Ketron expert, but most arrangers these days have some form of EQ per Part in the arranger itself. So separating the Part out through individual outputs may not be necessary, simply add the EQ internally…

You might also take a good listen to your PA playing a commercial CD of your preferred music with the channel set flat. Does it sound good, well balanced, not tubby or shrill? If the CD sounds like it’s going to need some bass EQ this might indicate you need a sub to fill in the low end. That might make the Ketron sound nice and full all by itself. Again, nowadays, most arrangers are set up to sound great through a flat sound system, you might find yourself not needing to go through all this…