Here are some websites with sample listening material that provide a nice introduction to - and focus on - specific composers:
Karlheinz Stockhausen - Stockhausen-Verlag, media files
György Ligeti - Tonbeispiele (music samples)
Isang Yun - Uni Mozarteum Salzburg (samples, discourse) (German)
Karlheinz Stockhausen - Stockhausen-Verlag, media files
György Ligeti - Tonbeispiele (music samples)
Isang Yun - Uni Mozarteum Salzburg (samples, discourse) (German)