I 'll second East Coast as close to AC and good and I do not believe there are any dive operators/stores on the actual island of AC so getting 'closer' isn't really viable. My other half DM's for East Coast on the boats mentioned and if you do plan trips, let me know dates and I'll let you know if he is scheduled to work the trip. You're right Ed - the Larsens (the Atlantus) have seawater in their veins! There are also a couple places to hang out - drink and eat - in Gardiners Basin where the Atlantus is berthed.
Not sure what month you are coming in, but be aware there is the potential to be blown out by storms in the later part of the summer - late July, August & into Sept. Trips are often called off the night before or morning of, depending on forecast and conditions.
My summer home is about 20 miles south of AC, so if you have any questions, I'd be happy to assist.
Regards, Jersey