I am also Marriott silver and I don't get access to the M lounge for drinks, snacks, dinner. I suggest you confirm this with Marriott. But I think you will probably have to explicitly reserve a room which includes this lounge availability in the room fare.
Dear Rui P,
Thank you for taking your time and giving us the opportunity to answer your question,. We do not have a suite at this property here at Durham Marriott City Center. We can do our absolute best to get you into connecting rooms if that will accommodate your need. Please let us know.