Now, I read your thread where you are looking for speakers with alittle more bass that what your today ones gives you.
Of course that the best way to go is to integrate two self powered subs to your room/system where you can take the subs signal from your input speakers and due that the subs are self powered and has its own crossover filter will not alter the impedance that are " seen " by your amplifier.
The CW IV has a high problem in its woofers because handled a to wide frequency range that develops a very high Intermodulation Distortion levels that goes against MUSIC .
Regards and enjoy the MUSIC NOT DISTORTIONS,
R.