This is optional and may well slow things down especially if you gave the cube lots of segments but add a hypernurbs and drop the particle geometry into it, this will give the particles a smooth round look

OK material for the particles is basically the same as the sphere without the noise and different colors

Drop the mat either onto the cube or the geometry

Just for fun lets add a freeze to the particles, to stop their motion for a short time, we need another action timer

freeze is found under TP dynamics

In xpresso add a freeze input to the new freeze we just created

Connect the particle port to the PPass node we created earlier

Sorry this is not too clear but link the action port of the action timer to the freeze port of the freeze node

Now link the time port of our original time node to the new action timer

In attribute manager set the freeze from frames 100 to 150