If you think of Terry Riley as the composer who restored simple pleasures to contemporary music with works like In C and A Rainbow in Curved Air, you might be perplexed by the angularity and chromaticism of these recent pieces. It’s hard to follow where he’s going when he wanders so freely over the harmonic and stylistic map. Composed over the last six years, each of these 28 pieces has a title that starts with a different letter of the Spanish alphabet, and Riley evokes Spanish guitar music with intricate passage work, Latin dances, and flamenco strumming. David Tanenbaum, who commissioned these works, gives them articulate and poetic readings even at their most unwieldy. He teams up for stunning duos with violinist Tracy Silverman in one suite, and percussionist William Winant joins him in another on tabla, marimba, Peking opera gongs, and other instruments. Riley’s talented son Gyan, who brought the guitar into the Riley household, joins Tanenbaum on Zamorra.