This is how I set up my Tyros 4 to get the harmony as a descant. You may chose other voices, trust your luck,
This is the MAIN SCREEN, Note the volumes set. You may choose to adjust these.
Go into the Functions menu and select the Style setting.
Turn OFF the accompaniment. This is not necessary but I don't like the strings as provided by Yamaha.
Press Direct Access and then the Harmony/Echo button.
Set the Type to Country Trio and assign the voice to R3 (important for the descant.)
Now go and make a noise not forgetting to turn on all the voices.
If I have missed something please let me know.
Den.