Surprised

kosst, with all due respect, you are far from correct. If you’re talking about inexpensive bookshelf speakers, their performance doesn’t justify the money agreed, however, spend good money and get quality products and a REL will integrate nicely. Most quality bookshelf speakers are two-way, good to somewhere around 50Hz give or take some. My Paradigm Signature S2’s are good to 52 (±2dB from 52 Hz - 45 kHz) as per manufacturers specs. Therefore I crossover my R-528 at about 60Hz.
Floor standers (towers) are only good to roughly 40 Hz. Not that much difference. Also it’s important to have the sub the same distance from your listening position assuring there is no phase shift. A common mistake is stuffing a sub in the corner and their mains are 2-3 feet forward of them. This creates a timing issue as the mains will reach your ears before the sub.
The REL has the ability to seamlessly integrate at pretty much any frequency necessary. Too much overlap and it sounds like mud. Not enough and there’s a disconnect. Trick is to find that sweet spot. Don’t forget, volume has a play in it as well. The beauty of REL is as it’s connected high level, they get the same signature as the main speakers. I highly recommend a left and right subwoofer to compliment the left and right mains. With a REL integrated with each main speaker, it will blow away most floor standers (towers) without a sub. Although Focal speakers are very nice, I have a set of Utopia’s in my truck and they are outstanding, it’s all a matter of taste. I’d be careful making direct global comparisons without hard data to back it up otherwise you’re just stating an opinion.
Btw, my room is 13' x 15' x 8", hardwood floors covered by a rug. a sofa 4" from the rear wall, a coffee table and the only room treatment is some sound deadening foam center between the mains.

Here's my system;
Paradigm (Signature S2- Front L&R): (CC-690- Center): (Studio 20- Surround L&R)
REL R-528 (FL & FR, RL & RR, 3 total) / REL T-9 (CC)
Anthem P5 & AVM 60 / Oppo BDP-103 - Blu Ray
Interconnects: Audioquest, King Cobra & Yukon
Speaker cable FL & FR: Transparent Audio / AC cords: Audioquest NRG-4 & WyWires Juice II

I had floorstanders in a room with about the same dimensions as your room, so 14' x 15' x 8.' My speakers go down to 30 Hz and driven with the right amplification, the bass was excellent. Then I moved my system into a large open space, and while I gained some detail, where's the beef?

I added subs, and I'm still running my floorstanders full range. I use my two preamp outs for the setup. The sub amps have all the controls necessary to set things up any way you want. It's all there now, plus a wide open presentation I never had before.
Kenny

@oldschool111,
The big difference between the floorstanders  and bookshelf is not 
only bass, Most of the bookshelf is 2 way LS,   and loosing nice
mids, is the shortcoming, The best 2 way speakers is 3 way speakers,
The tweeter and woofer are not design to get good mids, 
We design all my speakers based on wideband drivers and get 
excellent vocal reproduction , like live    

Many years ago had 7.1 system with a sub the sound was rubbish, Moved to 2 floorstanders with a sub to found out it’s extremely difficult to get the sub tuned correctly now my Proac floorstanders go down to 25 Hz and driven with the McIntosh really making the sub unnecessary.Bookshelfs in principle can’t produce full body sound as floorstanders neither low bottom end unless you you’re buying extremely expensive high end bookshelfs that obviously will reuquier expnensive powerful amplification,cables and stands.

Well, I  own a DEQX Preamp and one of its features is a very sophisticated range of controls to intergrade the subs (JL F-113) very nicely.

ozzy