Original: His management company was named NEMS Enterprises, after his family's music stores, called NEMS (North End Music Stores).
Simplified: This was named NEMS, for North End Music Stores, and Epstein became its boss. Epstein started a management company, NEMS Enterprises (named after the music store), who later signed up the Bee Gees, Jimi Hendrix, and Cream.