There are several ways to pronounce Latin; the Ecclesiastical (Church Latin) pronunciation is probably called for in this case. In this system, vesperae solennes would be pronounced VES-peh-ray so-LEN-ness (where "peh" represents a syllable like English "pet" without the 't').

You could be describing opera or an operetta or a work in musical theatre.

Concerto

The cast of Messiah - 1999 includes: Brian Asawa as Solistes - countre-tenor Charles Aznavour as himself Patrick Beaugiraud as Orchestra - oboe Laurent Bourdeaux as Chorus - bass Diane Chmela as Orchestra - violas Julian Clarkson as Chorus - bass Fabienne Colson as Chorus - soprano Simon Dariel as Orchestra - violins Nadine Davin as Orchestra - violas Lynne Dawson as Solistes - soprano Lucas de Jong as Chorus - bass Laurence Duval as Orchestra - violas Sonia Findling as Chorus - alto Svetlana Fomina as Orchestra - violins Pedro Gandia Martin as Orchestra - violins Annie Garcia as Orchestra - violins Linda Gerrard as Chorus - soprano Pascal Gessi as Orchestra - cellos Mirella Giardelli as Orchestra - harpsichord Florence Goyer as Chorus - soprano Nicole Heaston as Solistes - soprano Charlotte Hellekant as Solistes - alto Frances Jellard as Chorus - alto Nicki Kennedy as Chorus - soprano Marinus Komst as Orchestra - timpani Fernando Lage as Orchestra - cellos Laurent Lagresle as Orchestra - violins Rachel Londop as Chorus - alto Marcos Loureiro de Sa as Chorus - bass Michel Maldonado as Orchestra - double bass Vincent Malgrange as Orchestra - cellos John Mark Ainsley as Solistes - tenor Penny Mathisen as Chorus - soprano Nicolas Mazzoleni as Orchestra - violins Yann Miriel as Orchestra - oboe Simon Neal as Chorus - bass Julie Neander as Orchestra - violins Ricardo Rapoport as Orchestra - basson Martin Robson as Chorus - bass Emilio Roman as Chorus - bass Sandrine Rondot as Chorus - soprano Russell Smythe as Solistes - baryton Anton Steck as Orchestra - violins Florence Stroesser as Orchestra - violins Christoph Timpe as Orchestra - violins Serge Tizac as Orchestra - trumpet Jory Vinikour as Orchestra - organ Verene Westphal as Orchestra - cellos Paolo Zuccheri as Orchestra - double bass