The Sennheiser 203's have good clarity and decent bass (depending on your preference)... a good bet.  i'd also suggest the audio technica ath-m30 as it definitely has a surprising bass depth and clarity.  i think you'll be happy either way.    

  if he likes how the m50's sound, id go with the m30's as well... i personally like a good soundstage with 80s rock so id suggest sennheiser hd515 (its open-aire) or the grado sr60s