Complex sentence: After some material had been written, auditions for a new keyboardist were held which involved around eight players, including Jean Roussel, Nick Glennie-Smith of Wally, and Greek musician Vangelis.
Split into simpler sentences: After some material had been written, auditions for a new keyboardist were held. They involved about eight players, including Jean Roussel, Nick Glennie-Smith of Wally, and Greek musician Vangelis.