well, the preenfm2 itself is 4 voice multitimbral, that means you can assign four different instruments to 4 different "slots" on the preen fm. (i1 to i4)
you can then assign different midi channels from the global menu, so that each channel is only played by a specific midi channel, creating 4 different instruments. you can also assign the same midi channel to all instruments and play them all at once. or you can load 4 times the same preset into the instrument slots and detune each voice slightly to get nice chorus effects.
you choose i1 to i4 simply by pressing the instrument button just below the volume pot on the right side.
