Baroque composers were fond of concealing coded references and sly musical quotations in their work, and few did it with as much craft and zeal as Bach. Musicologists have long marveled at the many cunning ways he embedded his name in his music, and recently German scholar Helga Thoene delved into his six pieces for unaccompanied violin (BWV 1001-6) and proposed that the sequence of sonatas and partitas not only follows a complex key signature scheme but also a theological progression from Incarnation to Passion to Pentecost. She further claims that Bach intended the ciaconna that closes the fourth piece, the D Minor Partita, as an epitaph for his first wife, Maria Barbara, who died in the prime of her life in 1720--her name is encrypted in the ciaconna's opening bars, and the partita contains hidden quotes from Bach's own Easter hymn "Christ lag in Todesbanden" ("Christ Lay in Death's Bondage"), implicitly linking the apostles' hope for Jesus' resurrection with Bach's desire to see his wife alive again. With this program, Baroque violin virtuoso Christoph Poppen and first-rate English vocal quartet the Hilliard Ensemble intend to make Bach's method plain by interspersing the five movements of the D Minor Partita with the chorales he quoted or took inspiration from. The concert reprises the contents of their new CD on ECM, Morimur, and shares its title--an allusion to the phrase "In Christo morimur" ("We die in Christ"), part of an invocation of the Trinity. The centerpiece of both is the ciaconna rearranged for Poppen and the Hilliard Ensemble, as close to a musical proof of Thoene's thesis as anyone is likely to get: much of the movement is still a violin solo, but during Bach's quotations from the aforementioned chorales, the four voices enter in a rich interplay. Doubtless not all listeners will be equally prepared to appreciate the musicological back story, but Poppen's expressive, doleful playing and the clarity and ardor of the Hilliard singers--countertenor David James, tenor John Potter, and baritone Gordon Jones, joined by guest soprano Monika Mauch--should be enough to enchant anyone with ears. Thursday, April 25, 7:30 PM, Saint James Cathedral, 65 E. Huron; 773-722-5463.