Thanks for the suggestion. Although I am not completely against adding a second sub I am trying to avoid using up any additional space. I do think the factory B&O system is pretty good for my situation it just needs a small touch more. That is what attracted me to this thread.OPs choice is not a better option. I went out and found the highest efficiency (103db) aftermarket 6x9" I could and it wasn't a meaningful improvement over the stock sub. What Ford put in there is actually extremely well suited to its purpose. You are better off adding a second compact sub to handle the lowest frequencies and leave the B&O sub active to blend into the stock speakers.
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