Hey Marco,
I could go along the list of needs and check each one, but I stick with the selection idea for now:
Why is that a lot of work, even with 1,000 or 10,000 fragments? It isn’t! The main work is the five materials, right? ;o)
How to do it?
Switch off the Displacer and the “Random Effector.1”
Then go to the “Random Effector” set its displacement from point to polygon and increase the Position Z value to 5,000 or whatever makes sense to separate them. (You need to be in Edit Window>Configure All>“Deform Editing” checked on) It might need the same parameter than Effector.1, so perhaps you use a copy of RE.1 and set this to Deform Polygons and any other effector to off!
With the STar.1 object active, use the Rectangle Selection with “Select only visible” to off. Go to the top view!
Create you five groups with five quick selections (incl. Selection Tags) and apply the tags to the five materials. Doable under a minute. The movement in Z is precisely the
Set the random Effector back to point and the Z value to the one used before, etc.
All the best
Sassi