Patristic text regarding the role of the psaltis.

I am looking for specific Patristic citations regarding the role of the psaltai (other than Laodicea 15- I already quote that one extensively. I am dealing with two individuals who are trying to get rid of the psaltai and replace with congregational can belto. We've isolated the problems down to only two persons, but they seem to have the bishop's ear and I'd like to line my ducks up in case I need to.

JPP