It turns out that the problem with assembling a concert of the vocal music of William Byrd  is the sheer abundance of superb but lesser-heard compositions by the English composer. Musical groups around the world are commemorating Byrd’s death 400 years ago in 1623 by performing his spectacular works. But thanks to diligent sleuthing by Artistic Director Evanne Browne, audiences attending Seicento’s performances Nov. 17-19 will hear some of Byrd’s unexpected works. Joining Seicento’s  36-voice chorus are five instrumentalists playing violas da gamba—bowed instruments popular in the late 1600s but rarely heard in today’s concert halls. Concert features:  viol consort players Zoe Weiss, Sarah Biber, Sarah Graf, Karl Reque, and Adaiha MacAdam-Somer; singer soloists Gabrielle Razafinjatovo, Santiago Herrera, Hannah Baker, Deborah Kauffman, John Butterfield, Jonathan Raabe, and Derek Berger.