Possible Clues:

• Religious chorus, perhaps
• Singing group of very high quality right for church
• Those with strain in voice, one being choked by endless work
• Singers in church knocking back port
• Group of angels, maybe
• Cathedral has one: it rates the tops
• Hymn presenters
• No end of hard work I put in for part of church
• Van Morrison employed the street kind on a 1970 album
• Mississippi Mass, for one