The way the MX88 works is a bit different from the CP4 Stage, although there are some similarities that will help you understand.

Like the CP4 Stage you are in Performance mode... the CP4 Stage is three Parts (Main, Layer, Split)
The MX88 has Parts 1 and 2 that can be Layered or Split in a Performance. When the Performance [SELECT] button is lit, you can advance through programs one after the other

Additionally, each MX Performance has fourteen other slots for Voices... Parts 3-16 in each Performance. So that for stage use, you might put several of your "go to" Voices in Parts of your Performance. You can "quick access" 16 Voices in each of the 128 Performances.

How you actually assemble your data for use on stage can be a combination of moving between Parts of one Performance... using the 1-16 [PART SELECT] buttons; and moving to an entirely new Performance setup.

When you activate the [PART SELECT] button you can seamless switch between the 16 instruments you've selected for this Performance, by just touching the numbered button [1]-[16], this makes performing and changing instruments a breeze. And by linking Part 1-2 you have a quick way to activate a Layer or Split.

If you are going to need Piano, strings, synth lead, organ, and big brass on the first tune, you can place these in Parts 1-5 of a single Performance.

Performance Direct Selection
In a similar method to the CP4 Stage, you can place the MX in Performance Direct Select where the sixteen right front panels give access to a set of sixteen direct selection buttons:

While the [SELECT] button is lit
Press [SHIFT] + [1] to access the first 16 Performances, then select any one of those via buttons [1]-[16]
Press [SHIFT] + [2] to access the second 16 and so on