Use Amigos Del Mar for your short dives and night dives to the preserve.
I do not know any of the groups that take you to the outer sites.
The Blue hole is a long trip for a short dive and in my opinion was nothing
more than a notch on the belt.
Take a day trip to one of Mayan ruins it is well worth it.
Hire a private guide to take you fishing and show you some back area stuff.
PS - Don't know about the DIN valves, might want to bring an adaptor