Brace yourself! It’s Icelandic composer Jon Leif’s “Saga Symphony.” Scored for tuned anvils; stones; whip; shields of iron, leather, and wood; great wooden containers played by large hammers; and six ancient long horns, or lurs, the work is an intriguing blend of extravagance and austerity. We greet our fate with courage and stoicism, this Sunday at 10 pm.