splitting the voices to each one separate

Explode?
You must have a separate blank staff underneath for each voice. However, the structure of the grand staff presents some problems.
Suppose you have four voices on the treble staff and four on the bass staff.
So: add four pianos for each treble system, delete the bass systems on each, and copy the treble notes to the first of the new pianos. Then apply "Explode."
Add another four pianos, delete the treble systems there for each, copy the bass notes to the first, and "Explode" again.

Another way if you have really written all in different voices:

• Add four pianos with grand staff
• use the selection filter to separate the selection for the different voices.
• copy the notes, set again "all" in the selection filter
• paste them in the first of the new piano stave
• do the same with the other voices and paste into the other new piano staves.

Also "Select more... / same voice" can be used.