Try La Parillada, I used to eat there on a regular basis, you can sit outside under a thatched roof, the staff is excellent and the food is fantastic. It serves your bifstek and yuca on a wooden cutting board and the flavour is out of this world, of course, there are other choices on the menu. Also, and I am sorry for this, but I can't remember the name of the place, but it is on the Malecon and if you take the street just past the baseball stadium down to the Malecon, it is just a few blocks down. It overlooks the water, and serves great Dominican cuisine and is a local joint!! I just wish I could remember the name, but maybe one of the other DR1's can supply the name.
Chris and Mady's is a really good restaurant as well, but I don't know if you want to travel all the way to Cofresi or not.
Also, there is a restaurant directory on the home page of DR1 that will give you some suggestions as well.
Whatever you do, try to get out there, staying in an AI, you could be any where in the world, you must leave the resort to get the real feel of being in the DR.
Enjoy your trip
Marlie