I am using an XP-80. So I don't know what all the 50 can do. But, each patch is made up of different tones. You can edit each tone of a patch. I suggested taking one or more of those tones within the patch and detuning them a little. The XP-80 also has a random function where it will change the pitch of a tone slightly or radicly, depending on how extreme you set it. On the XP80 I can get to it by pressing F2 button twice. For the XP50 I have no clue whatever how to get to it, but I would assume it does it.
Chorus is a type of effect; a doubling effect with a slight pitch fluctuation. You can also set a delay time on the chorus as well, which will give you similar, but not exactly, the same concept as Dnarkosis described