Possible Clues:

• Freely I stream their wonderful music-making
• Joiner turned up with three experts
• Excellent conductors
• Conductors from West maybe on second short tour
• A mister, extraordinary, may be in this group?
• West Street Providence, say, for brilliant performers
• Remit as difficult for great composers
• Aces concealed in shirt seams put back
• More than one conductor's no good in jazzy ragtimes
• A term is concocted for expert players