Bob hit the nail on the head. IF you notice that the low frequencies are obviously coming from the sub then the sub is not integrated. It's that simple. If the salesman can't make this happen then I would not buy a sub from them. I also agree with his recommendation of a REL strata (I own one, and I really can't tell that it's producing the bass until I switch it off). You can get a used REL strata for under $900.
Salesmen who sell subs according to power rating or ability to knock pictures off the wall are selling for home theater, not music.
Salesmen who sell subs according to power rating or ability to knock pictures off the wall are selling for home theater, not music.