noun
vocal sextet
A musical ensemble of six singers, or a piece written for six voices.
彼らは六重唱で美しいハーモニーを奏でた。
They performed a beautiful harmony as a vocal sextet.
六重奏 refers to an instrumental sextet, while 六重唱 is specifically for voices.
Compound of 六 (six), 重 (layer, multiple), and 唱 (singing). The reading ろくじゅうしょう follows standard on'yomi patterns.