As you can see, the BASS response on the STS is about 25-30Hz @ -3dB, which is a lot better than most so-called stand-alone subwoofers you see at Best Buy.
http://www.stereophile.com/floorloudspeakers/808dt/index4.html
I had a stand-alone NHT 10" subwoofer that was specified as 27Hz bass-response. I sold it to my little brother. But that thing (even at 27Hz) shook my walls very violently - the same walls I now watch movies in.
So the Mythos STS will give you VERY VERY GOOD bass response.
Just don't compare it to bigger badder subs from SVS, HSU, Epik, or DefTech's bigger subs that can go below 20Hz.