One other suggestion if you like that sub. If you don't see the problem when you open the amp, why not just use another amp with it? You can cover the old amp opening, run speaker wires to that cover and have another amp sitting by the sub, run the RCA to it, speaker wires directly to the sub, and you are in business. After all, you have nothing to loose and may recover your sub by an external amp.
Or, you can also buy an amp for sub use, like one from SVS perhaps?