He is the founder and leader of the ensemble Ritornello which performs music of the 16th and 17th centuries for voices and a great variety of instruments.

He has collaborated internationally with ensembles such as Musica Antiqua Praha, Capella Regia Musicalis, Bornus Consort and the Tölzer Knabenchor.

Their instruments are historic or faithful reproductions, including lute, theorbo, Baroque guitar and violins, hurdy-gurdy, Renaissance bagpipes and trombones, organ, dulcian, flutes, viola da braccio and viola da gamba.

[3] In 1998, Pospíšil recorded Jakub Jan Ryba's Česká mše vánoční (Czech Christmas Mass) with Gabriela Eibenová, Magdalena Kožená, Jaroslav Březina, the Calmus Ensemble and the Capella Regia Musicalis.

[4] In 2004, he sang the bass part in Bach's Christmas Oratorio in St. Martin, Idstein, with Katia Plaschka, Franz Vitzthum and the orchestra Antichi Strumenti.