Simplify the following text for a Grade 9 native English-speaking person.
Original: Chief conductors since then included Rudolf Schwarz , the composer Andrzej Panufnik , Boult in an emergency return for a season after Panufnik 's sudden resignation , Hugo Rignold and Louis FrÃ maux .
Simplified: Chief conductors since then included Rudolf Schwarz and the composer Andrzej Panufnik .