The Diamond Club is bigger than the concierge lounge, plus it has a balcony area with tables. The Diamond Club holds around 85 people and is located on deck 14. If it's too crowded they close it and open the Labyrinth Lounge on deck 3 between 5pm and 8:30pm for the entire week. Only Grand Suite and above guests are allowed in the concierge lounge.
>Edited to add pictures<
Sonny