n without using high pass filtering, matching the stand alone subs to the speakers presentation is impossible.
@m-db is not impossible, on my specific case the subs and the speakers are manufactured by the same company, speakers crossover and speakers themselves are tuned to the 4 subs and integrated with dsp amps.
The beauty of it is you can follow the designers integration recommendations or you can try to play and better the designers intentions (not that you could have a real chance to improve it much) tweaking dsp etc.
As and added convenience 2 out of the 4 subs share the same footprint as the speakers so no extra space needed. I have to add that I personally like the idea of separate subs from the speakers better in terms of location, true you need some extra real estate but not much and you have more options to locate the subs, you can even tweak with the vertical plane and locate 1 or 2 in your ceiling if you are up to the task (I am not)
In the case the designer is not the same you still can find speakers with proper integration, most speakers are ranged starting at 50 hz 60hz you could use dsp to match these values as well or modify the xover like you mentioned