The Tyros should work as a vocoder..Just set the midi channel preference to the track that best delivers the proper data..As a example , Tune 1000 sequences transmit the data on channel 5..You can also assign the vocoder to your playing hands and voice the harmonies..You can also select a channel like 16 and record your own chords and voicings ..Re-save as a added track to your sequence..

I like the Roland harmonists the best..It analyses the files and does a superb job of harmonizing..By far the best I have used..