I'm a fan of the Schertler Dyn-G, which sometimes can be found used for around $200.
Completely external, removable, great starting point for a remarkable plugged-in sound. You could keep the Fishman and blend them externally, or just forget about the current system altogether (leave it in or not).
If you want to close the barn door, I bet any decent local luthier/repairperson could make a nice removable "plug" out of a rosewood veneer and some magnets
