@james633 , You are not even 50% of the way there yet. Your speakers are capable of even better performance!
The woofer in the 4367 is crossed over to the horn at 700 Hz. That covers a huge amount of the mid range. Remember, middle C is 256 Hz. 700 Hz covers more than another octave! Do you know what Doppler shift is? That is when a car honks it's horn while it is passing you, the horn changes tone. That is what a woofer does when it moves towards you then away from you, it shifts the frequency of everything else it is reproducing. This is called distortion! This movement is most pronounced at very low frequencies. If you can see the woofer moving it is causing Doppler distortion. This usually occurs below 100 Hz. In the case of your speaker probably 80 Hz. If you have a test record with frequency bands you can see when this happens. Adding subwoofers to a system is not only to add more low end, it is also to lower distortion in the main speaker. With these speakers a minimum of two 12" subs is required and you have to use a high pass filter on the main amplifier, a full two way crossover. Digital is best. Crossover at 80 Hz. Do this and you will take your system a large step forward.