@jeres8860 , Your SCM 11s are lovely little two way monitors with very capable drivers. Adding subwoofers correctly to this type of loudspeaker takes them to an entirely different level of performance even better than most large three way floor standers. Because of the very small enclosures they have less trouble with enclosure resonance and diffraction leading to more precise imaging. Adding subwoofers can drop distortion dramatically at volume and increase the headroom 10 dB. That is twice as loud! That is like getting an amp that is three times larger.
Doing this wrong will just f--- things up. To do this correctly you have to get two subwoofers. Place them just inside each SM 11 up against a wall and try to keep all the speakers on the same radius from the listening position. I suggest 12" drivers. If you are a handy guy get kits from Parts Express and use the money saved to get a digital preamp with bass management. The MiniDSP SHD is only $1300.00 To drive the subwoofers get a commercial sound reinforcement AB amp like a QSC. It has to have a balanced input. If you want to go ahead with this and you have any trouble feel free to message me. Believe it or not, all this will cost you less than one 13" JL Audio subwoofer!