I'm the head of the technology team for my church in Palm Coast, Florida, and we have about 4-7 singers each Sabbath as part of a Praise Team (give or take.)
We typically play piano tracks in different voices (soprano, alto, etc) and we have each person listen to their track and learn it throughout the week (I wish).
Then, we bring them together Friday night to harmonize and prepare to sing on Saturday.
But, since our singers are quite novice, they struggle to follow the piano tracks, so what we did was put each track of the .midi through a vocal synthesizer (see samples in blog post).
Figured some of y'all might be interested in seeing some of it. Granted, after the initial introduction, the blog post does go off into the technical details of the implementation, but figured some of y'all might still be interested.