Marco, George, The Tune 1000 SMF's with channel 5 assigned utilizes vocoder mode..

Marco this is why the harmony stops when their is no data being sent from any particular channel..

Although the Roland can also work as this in vocoder mode..Roland uses a better concept sending chord data to the preset harmonies..allowing you to switch on and off at will..The harmonies are always ready to sound...
You may want to experiment with the piano track usually channel 3..It is usually the busiest channel ..3 or 4 notes....