OK. Here goes ;)
1. load a voice.
2. goto page 7. Press alt/ctrl+x to copy. select next voice. Press alt/ctrl+v to paste this voice as a reference - do this 4 times so voices 1,2,3,4 are the same
3. goto page 3 voice. you should see the four voices. click to select the first voice. At the bottom SET NPHONY to 4 - voila you should have 4 voice polypony