I see, well, yes if you're running Eminence drivers yes, they do have, and are designed to have, output into the midrange. But, they are not true HiFi speakers; they are Sound Reinforcement / Guitar Amp speakers (depending on model; I didn't look yours up) and often don't have particularly good extreme low bass response. In a live music situation, output below 100 Hz is a problem to be corrected, not a feature to be exploited, so most music speakers are designed to limit extreme Low Frequency output.
I don't mean to imply they are not good quality; quite the opposite. But they were designed to *create* sound, not *reproduce* sound, and there is a difference.
A Bass Guitar with standard tuning will have a Low E at about 41 Hz, but many players do not use standard tuning, and if you were to ask what frequency you would need to meet to be able to play back every bass guitar on the available music today, you would want to be flat into roughly 30 Hz. If you don't need the ability to play low synthesizer notes, or don't like Bach and won't be listening to Pipe Organ recordings, you could stop there. If you do want to play one or both of the above "exception" instruments, then you might even want to place your Low Frequency rolloff to begin as low as perhaps 16 Hz.
So, there is some method to the Subwoofer madness.
There is a corollary, though, and that is humans don't necessarily need to hear the fundamental with low bass notes; we can accept a resonant peak somewhere in the 2nd harmonic (2H) and sometimes 3rd harmonic (3H) range and enjoy the result. Say, the system reproduces mostly 82 Hz for your low E 41 Hz fundamental. That's how low-fi speakers, and more than a few HiFi speakers, still manage to produce a listenable result. A lot of smaller driver speakers ... you know, the ones with 4", 6" and 8" drivers we are suggesting would be best for mid-bass and above ... do exactly that, covering their inability to play true low bass notes.
I haven't suggested a subwoofer is necessary in a system, and certainly using 12" drivers in a full range system is one way to ameriorlate that situation. That might be assigned the task of the very lowest notes, or it might be asked to cover a wider range, but it's usually a matter of pick one, not both.
But just so you know, subs are not new to me, and I built my first subwoofer system in the 1970's. I've used 15", 18" and even the legendary Hartley 24" driver in some builds. Without seeing your speakers I am none the less confident that I've built ones that were bigger. We even built one where the entire basement was the inside of the enclosure, the subs firing into the floor of the room above.
That was a time when we did use large woofers in not just 3-way but also in 2-way systems, but it also was a time when good, synthetic cone 6 and 8" drivers from companies like Son-Audax and KEF were just entering the market.
What happened to me is what I'm suggesting you should consider ... that a great midrange, where perhaps 80% of the musical information lies, frees up the space for a great woofer. It was evident then, and has evolved since from black magic and a certain "art" in a speaker designer's skill set, to science. It is really not difficult to design a good DIY full range system today, although it does take effort, it's certainly within the realm of most relatively handy people's abilities if they apply themselves.
The point being, however that both drivers perform better than either would alone. Just some food for thought. And the jury was out, came back, and gave it's verdict a long time ago. It's really not even brought up anymore in serious loudspeaker design circles.
With regard to the size of subwoofers, they are today much, much more compact than what was achievable in the past for the same low frequency response. So, although relatively large, they are not large in the grand scheme of things. And if you get above perhaps 120 Hz, maybe even a little lower, you can do that in a box the size of a shoebox or smaller.
Nor do low frequency notes need to originate in front of you (or wherever the setup requires, such as a 5.x or 7.x, etc system) as your front stereo pair do. They are not directional, up to a point.
So, another reason why they are often recommended ... you can put them almost anywhere in the room, with certain limitations that are important but can be overcome with relatively small changes in location, up to about 80 Hz.
Anything above that frequency, and humans with both ears in functional condition will start to locate the source of the sound (direction). So your sub can't be off to one side AND have response above about 80 Hz (the exact number will vary depending on the crossover characteristics).
The smaller and less obtrusive the stereo main pair are, the easier they are to place. Placement is a critical criteria in system Sound Quality (SQ).
That makes a subwoofer with "satellites" a viable option for the modern home. Now, some people ... I suspect you are one ... don't have an issue with large loudspeakers in the room. Not everyone is lucky enough to be in that position. But it's just one more reason for the popularity of a 2.1 or larger system configuration.
Please note I am not referring to what are marketed as subwoofers; I am referring to actual subwoofers. There are a lot of products in the marketplace that are incapable of actual sub-bass reproduction (20~40 Hz) along with low bass that wear the name.
Advertising is a shady game. Somehow we aren't supposed to say "lies" out loud, when we are fed lies by copywriters. But that's the reality of the world we live in; the companies that are selling you products are not actually interested in your best interests, they are interested in converting your cash to their cash. Some do it more ethically than others, but fundamentally they are all engaged in the same game.
I have always said here, and elsewhere, that it's not my system, it's yours. That does not mean I won't give my honest advice, and the benefit of my experience, when asked and I feel willing to reply. I do ignore many, many posters here not because I'm trying to be rude, but because I am not interested in giving half an answer when I could give a full one. Doing so requires my attention, which is limited, as I do have a life. So every once in a while I'll engage in discussion with someone, such as yourself.
It does mean, however, that the ultimate judge of what is right for you is you. If you are happy, then you have achieved your objective. I just don't understand why you would ask a question you have no intention of considering answers to. You seem more interested in defending your ideas and the existing system you have rather than seeking answers regarding how to improve what you have. Maybe I am reading your responses wrong, but it seems to be that way.
"Main" (as in "primary") is used to refer to audio equipment; "Mains" ( plural form) refers to the AC wiring that runs through your home.
Everything has to be taken in context. There are people willing to trade extreme Low Frequency reproduction ability for some other aspect ... perhaps they want a killer midrange, use a full-frequency single crossover-less driver to achieve that, and are happy with the result.
Others ... especially those who want to combine a music and movie playback system into one ... want the widest frequency response from the bottom to the top with visceral power and are willing to give up that last tenth of detail that having crossovers in the system will tend to kill.
Neither is more "right" than the other, they are just different, and there are a dozen other system goals that compete with one another; give a little here, take a little there. Knowing what you want from the audio gear is the most important first step in building a system.
Many people have no idea what they want, so if offered advice is going to be any help at all, you have to start with helping them find that answer, because no system you build without that answer will be satisfactory (unless you just don't care).
I am not convinced you have answered that question yet, or if you have, you've kept it from us, which is a mistake.
