BOZ SCAGGS  The genre-blending genius takes on classic songs in a historic studio  By Jeff Tamarkin Play Boz Scaggs’ 44-year-old debut album, his 1976 multiplatinum megahit Silk Degrees, or his pair of standards records from the past decade, and one constant emerges from his music: He remains true to his vision, finding that sweet spot where R&B, pop, jazz, blues and rock intersect and then customizing it. Scaggs’ attention to detail, level...