Click on the "Edit" menu and select the "Filter" submenu. A list of additional options will appear. Click on "Edit Instruments."
Select the choir audio instrument that you have currently applied to your voice track. In the option on the far right of the dialog box, select "Edit Instrument."
Locate the playback defaults section. You will see the current audio playback defaults under the "Best Sounds" option. Click "Choose" underneath that dialog box.
Click on "Voice" from the General MIDI box and select the new voice default you would like to use. Options available include "vocal oohs," "choir aahs" and several voice classifications from soprano to bass.