Often referred to as monuments of music, there are score collections whose call numbers begin with M2. When citing a M2 score/volume/work, use the style for book in a series, Chicago 14.25. Listing the series editor is optional. Volume title is italicized but series title is not italicized. If you cite an individual work from a volume, that title is italicized as well (see Schneider and Schumann).
Examples of Bibliographic style citations:
Beach, Amy. Quartet for Strings (In One Movement), Opus 89. Edited by Adrienne Fried Block. Recent Researches in American Music 23. A-R Editions, 1994.
Eccles, John. Semele: An Opera. Edited by Richard Platt. Music Britannica: A National Collection of Music 76. Stainer and Bell, 2000.
Schumann, Clara. Lied der Braut, Op. 25, No. 11. In Arrangements for Solo Piano, edited by Jonathan Kregor. Recent Researches in the Music of the Ninetheeth and Early Twentieth Centuries 56. A-R Editions: 2012.
Schneider, Friedrich. Die Jarhreszeiten. Text by T.L.A. Heinroth. In Topical Song Cycles of the Early Nineteenth Century, edited by Ruth O. Bingham. Recent Researches in the Music of the Nineteenth and Early Twentieth Centuries 37. A-R Editions, 2003.
Since we are only citing one individual work from the volume, we add "In" before the volume title just as we would when citing a chapter from a book.
Machaut, Guillaume de. The Works of Guillaume de Machaut. Polyphonic Music of the Fourteenth Century, vols. 2-3. Editions de l'Oiseau-Lyre, 1956.
Since the works of Machaut span the 2nd and 3rd volumes of the series, we can ease confusion about the multiple numbers by adding a comma after the series title and inserting "vols. 2-3."
Spohr, Louis. Faust, "Aire des Mephisto." In Die Oper III, edited by Helmuth Christian Wolff. Das Musikwerk eine Beispielsammlung zur Musikgeschichte, edited by Karl Gustav Fellerer, vol. 2. Laaber-Verlag, 2005.
If you do choose to include the editor of the series, then you must add a comma after the series editor and "vol." before the volume number.