Sound Improvement

Couple months ago I purchased a JL subwoofer which is amazing and i don't regret it at all. I was vacuuming the seats and found two speaker covers under the seats and notice that the speakers or 'factory subs' barely push out any sound at all I already have enough bass and shaking from the woofer in the trunk but would it be worth getting two 8" subs or regular speakers under the seats?

Thanks