My main speakers don't benefit as much from subs as they are good to 20 Hz on their own. Obviously the limitation there is that you are locked into the manufacturers set up as the low bass isn't independently adjustable as it is with separate subs.
I also operate an audio system that incorporates my main speakers plus a pair of powered subs that are 3 dB down at 16 Hz and so of course had the opportunity to try my stereo set up along with the subs. Other than slightly boosting really low bass - which matters if you are into organ music - there wasn't much advantage to adding the subs over without subs.
Another system I have is one I'd really like to integrate a sub into - ML CLS, but electrostatics are a bitch to blend with subs especially with a smaller room.
Can't recall if anyone combined Quad ESLs really successfully with subs....