If this is for a church choir, and if the church has a "modern" organ that you could use, it may have better "built-in" midi than you're likely to set up on your PC. Many of the newer organs (15 or 20 years) have very sophisticated midi systems, that allow play-in and play-back with part extraction (if you put it in in parts) to play multiple channels independently.

Sort of a long shot, but worth a look if it's there.

John