A REL or other high quality dedicated sub will give highly accurate extreme LF bass. This is useful in the 20 to 50 Hz range if you have monitor type speakers (designed for very low bass distortion and consequently limited in bass LF extension).
I can only suspect that your speakers neither need a sub and nor would they be easy to set up with a sub; they would share energy in the same frequency range making a match difficult.
I can only suspect that your speakers neither need a sub and nor would they be easy to set up with a sub; they would share energy in the same frequency range making a match difficult.