In his Symphony No. 9, “From the New World,” Dvorák reflected back the bountiful and optimistic United States that welcomed him with open arms. Spirituals learned from the grandson of a freed slave and transcriptions of Native American melodies enrich this melting pot of European refinement and American earnestness. In the same way that Dvorák gave voice to his Czech homeland through folk-inspired symphonies and tone poems, the Polish trendsetter Karol Szymanowski liberated his country’s musical identity by crafting imaginative works for orchestra steeped in local traditions. The Scottish superstar Nicola Benedetti made a forceful case for Szymanowski when she recorded his First Violin Concerto at the age of 17, and now she brings that passion to the Second Violin Concerto, a seamless marvel of grounded melodies and lofty virtuosic flights.