Ivan Hewett talks to Harrison Birtwistle and Peter Hall about the role of music in their forthcoming version of Bacchai at the Royal National Theatre. Plus a discussion about thematic programming as this year's Proms season is announced and, as a new book is published on composer/pianists, Marc-Andre Hamelin celebrates the virtuosity of Godwosky, Alkan and Busoni. E-MAIL: music.matters@bbc.co.uk