The men of Sestina, Northern Ireland’s unique early ensemble are striding out on their own tonight, leaving the women, for now, in the wings. For this gender imbalance you can point an accusing finger, into the distant past, at various Papal decrees that forbade women singers in the church.Not good news for aspiring female singers of the time, though we should perhaps spare a thought for the promising young male altos, who were castrated in order to preserve their angelic voices. Today, happily enough, Sestina relies on natural talent as opposed to radical surgical manipulation for results. This concert, in the magnificent…