Sir Peter Maxwell Davies, is an acquired taste just like Birtwistle. Both went to college together, but both took different paths there after. Birtwistle stayed with his self found ritualistic style founded with his love for Greek mythology. Davies hibernated on a Scottish Island with his surroundings acting as artistic food. I must admit it took me a long time to realise just how good a composer Davies is. He is hard work but well worth it. With Birtwistle you know what you are going to get, with Davies you don't. Both simplistic and outrageous, his music can never be called dull... Always a big folk music element and a clear love for medieval church music, if you have never tried any PMD then you could do worse than these 2 recommendations.