With their colorful mix of rarely heard original repertoire and imaginative arrangements, the Pierre Boulez Saal’s “instrument-themed” concerts have been musical journeys of discovery. Following programs dedicated to the clarinet, oboe, and horn in previous years, the double bass takes center stage this season. The evening has been curated by Nabil Shehata, longtime bassist of the West-Eastern Divan Orchestra and chief conductor of the Philharmonie Südwestfalen. Together with five acclaimed colleagues, he explores the many facets of his instrument.