Casio CZ/ VZ/ FZ - Pro Series

hi, i'm new to the casio cz, as i only got one a couple of days ago. 
one of the things that attracted me to it is that it has 8 part multi-
timbrality. my only problem is that i dont know how to set a 
different channel for each voice. when i go into the midi settings 
for a voice and set it to m.mode and then change the channel i do 
this for another voice and all the voices are set on the same 
channel. if someone could let me know how to set this up i would be 
very grateful.
thanks in advance
ali