Yamaha DTXpress/DTXplorer/DTXtreme

Can somebody help me with the following: 

I don't understand the voices-thing fully. I assigned a second voice 
to the beauty snare (for experiment a completely different voice).  
But I don't hear any difference. So I thought, let's go info the 
voices layer menu. I experimented some with the balance of the 2 
voices. Not a difference at all. 

I suppose I don't understand things rightly. What is the concept 
anyway? For example, in the manual it says that the beauty snare has 
got 2 voices. But in the voice edit menu, when addressing voice 2, it 
says: no assign (that's the reason I assigned a different voice here, 
but like I said, I don't hear a difference).