spacial reproductionWhat exactly do you mean by that?
The subtle details that make up the recording studio, the reflections of certain notes off the walls or ceiling, the subtleties of a breeze or noise coming from a nearby building that ’frames’ the space of the original scene sonically. Those subtle sounds and noises reproduced in the mid bass and bass are what helps to recreate the original sonice picture.
RELs do that with their high level connections, and an adjustment system and filters that help you dial them in so they Blend with your main speakers seamlessly. In my experience RELs help you reproduce the music or soundtracks much better than your mains do by themselves.
...Or you could build your own set of 10 or 15 world class subs from scratch like @millercarbon says he has. ;-)