For me the easiest way to get connecting rooms at Marriott was to make a reservation for one person in one room. Upon check-in you have about a 90% of getting a connecting room.
At least that was my experience with Marriott in Louisville and Buffalo. It took Platinum status to reverse that trend.
I haven't travelled to Louisville in years and still have the room number of the connecting rooms permanently burned into my mind. Everytime I would hear it, I would ask for a change. Sometimes they actually even seemed to care and changed my room assignment!
Good luck.