The AGA sump is really designed for a fish only/ freshwater tank and to be used as a wet/dry filter. The amount of room available for a skimmer, calcium reactor, phosphate reactor, auto top off, and heaters is really minimal when you are trying to effectively run your tank.
Honestly, I would just get rid of that sump and get a 75 gallon tank which you can add baffles to. That way you can get a big enough skimmer (I'm thinking octo extreme 250 or 300). IME, two smaller skimmers will not be as effective as one truly able to handle your tank.