You have to activate the Voice Button. You'll see a preset list with 64 voices available. You can change that list to voices that you would like by first moving the cursor to the voice that you would like to change, then hit the edit button. Now you can scroll through the list of voices available until you get to the voice you want to put in that position of presets, let's say you chose Steeldrum, make your necessary changes (volume, octave, pan, etc) then press save & name it Steeldrum. You can do this with all 64 presets. Then from your controller you can choose the voice from the newly modified preset list that you would like to use. There is another way but you would have to have a controller that is capable of sending bank change messages in addition to program change messages.
I found it easier to modify the preset list with my favorite voices. Hope this helps. If you have any questions, I'll try to help.