In 2009, the Kostov-Valkov Duo gave their Carnegie Hall debut at Zankel Hall. In 2011 they won the Liszt-Garisson International Competition, where they were awarded First Prize, the overall Liszt Prize, and all the special prizes in the collaborative artists category. In 2016 they released a second CD, containing award-winning transcriptions by the Kostov-Valkov Duo of works by Franz Liszt, as well as virtuoso arrangements from the operas Carmen, and The Barber of Seville.