The members of Chicago institution Tortoise keep busy during the group’s long periods of inactivity: percussionist John McEntire works tirelessly as a recording engineer and producer at his studio, Soma, and guitarist Jeff Parker plays in countless jazz combos, both established and ad hoc, here and in his adopted home of Los Angeles (on Thu 8/8 at Pritzker Pavilion, he and Wilco guitarist Nels Cline will play the classic Paul Bley-John Gilmore album The Turning Point). But within the past year, the best record by one of Tortoise’s numerous spin-offs has come from bassist Douglas McCombs, also a longtime member of Eleventh Dream Day and recent substitute in the Sea and Cake. After a lengthy hiatus he reset his Brokeback project with a strong new lineup, and on Brokeback & the Black Rock they transform the band’s existing aesthetic—twangy, atmospheric, and wide open, evoking the American southwest as refracted through Ennio Morricone’s spaghetti-western scores—into a visceral yet crystalline rock-combo sound that balances the churning intensity of Neil Young’s Crazy Horse with the resonant chill of Tom Verlaine’s late work.