There are more Dixie Mafia members deployed in the area. If you want to reach the boss without alerting his men initially, you can follow the same route you took during your first visit. Enter the first door to the left to avoid the two gang members by the main entrance then creep through the western corridor up until the backstage. There’s a preoccupied gang member trying to get something from the cigarette vending machine so take him out and carry the body to the dressing room.
There’s another oblivious gang member taking a leak in the bathroom beside the dressing room so kill him then loot the weapon locker beside the stairs again to get a Tac-Vest. (This vest “replenishes” itself once in a while so you can loot the same locker whenever you’re nearby or when you need additional protection).
Go upstairs and take out the roving guard. You can ignore the two gang members taking to each other or lure one of them by whistling. Make your way to the office area and take out or ignore the two gang members sitting by the mini-bar.
Proceed to the office and kick open the door and unleash your bullets at Merle and his bodyguard. When he’s down, go to him and press circle to finish him off. Once done, the Prostitution racket will finally be secured.
You can now assign the racket to Cassandra, earning her first favor. This allows you to buy the Screaming Zemi (can be thrown to distract and lure enemies to its direction) She’s your only underboss at this point so you have no choice but to give the racket to her. However, as you take over more rackets and get more underbosses, you’ll have to decide who will handle what.