You may not have heard of them, but you know Elvis Costello and T Bone Burnett, right? They portray their long-time alter-egos, Henry and Howard Coward, in the new scripted Audible Original series “The True Story of the Coward Brothers,” with accompanying 20-track album that we’ll feature. The Costello-scripted, Christopher Guest-directed, three-part audio series and its accompanying album are arriving right on the heels of an expansive boxed set that includes a substantial portion of the 40 years of collaborations between Costello and Burnett. The six-CD “King of America and Other Realms” includes a remastered version of the masterpiece that is 1986’s “King of America,” along with B-sides, outtakes, live tracks and selections from the projects that Burnett has produced for his “brother” in the nearly four decades since.