Three Tutorials here on the Korg Pa4X showing how to 'balance' the various PARTS, and even to have some PARTS not playing at all. You can also replace a PART with one of your own.
Korg PA4X Style Tutorial Part 1: Style Edit Page, Basic Editing, Creating New Styles
In this video, it's how to create a 'bespoke' STYLE from a MIDIFILE.
Korg PA4X Style Tutorial Part 2: Converting MIDI files into Styles on the PA4X
And in this one he shows you how to create your own backing PARTS. Probably the most useful of these is to replace the existing BASS PART with one of your own.
Korg PA4X Style Tutorial Part 3: Recording Custom Elements for a new Style on the PA4X