The transition from Infant Phenomenon (as Charles Dickens dubbed a pint-sized headliner in Nicholas Nickleby) to grown-up professional is fraught with snares, but Benjamin Grosvenor seems to have come through with flying colors. A sensation at 11 years of age in the BBC Young Musician Competition in 2004, Grosvenor is feted now as much for his sense of poetry and lucidity of thought as for prestidigitation of the technical variety. His Barcelona program juxtaposes the Baroque gallantries of Rameau against the majesty of Beethoven’s Piano Sonata No. 4 (nicknamed the “Grand,” partly for its half-hour duration), then transitions to Liszt for a wispy lullaby (“Berceuse”) and the stupendous Piano Sonata in B minor, which bewildered the composer’s contemporaries no end. It’s secret agenda (Faust? Paradise Lost? A musical self-portrait) remains a subject of lively debate. —M.G.