London's West End is the perfect springboard for stage musicals on their way to Broadway. A great advantage for British authors. More and more Americans use it too. Duncan Sheik, the Tony Award winner for “Spring Awakening”, and Roberto Aguirre-Sacasa (“Spider-Man: Turn Off the Dark”) mounted their new show “American Psycho” at Almeida Theater in London. The musical is based on Bret Easton Ellis’s 1991 novel of the same name about an investment banker who's also a serial killer. He will be singing and dancing amid spatters of blood in this musical adaptation at Second Stage Theater starting in February, executives there announced Monday.