With surfgate boats the only time we add extra weight we drop a sac in the walkway. That is about all we ever do. 750 in the rear and the nose full. you can try boat speed and a little more weight. Bring a few extra people out next time and have them sit in the center and a few big dudes stand in the walk way to see if that helps before you go buying another ballast bag.
I really would demo some different boards. that Koal longboard is thick but I think you just need a bigger board. I would suggest you try and borrow or demo a few larger size boards and ride the same wake. We would not have sold you a 4'10 longboard at 215. I would have suggested the larger one. So give the 4'10 to your wife and get you a new ride.
The current setup you have should work. I really feel it is more of a board issue.