Possible Clues:

• Hip-hop trio with the album "Paul's Boutique"
• "Licensed to Ill" hip-hop group
• Rap group with the classic 1986 album 'Licensed to Ill' ... or a description of 17-, 24-, 48- and 57-Across?
• "Licensed to Ill" rap trio
• Hip-hop trio in the Rock Hall of Fame
• Group whose members include Mike D