multiple subwoofers are not always better. if u have a budget of lets say 1000€/$ it might be better to go for one good one instead of two for half the price. The lower you go on sound ( 20hz - 35hz ) the more important becomes raw power that the subwoofer can deliver. If u go higher ( music rarely goes under 40hz and stays around 50hz-60hz alot ) the more important it becomes that your driver can play accuratly and has good dynamic range.
As i did write above, subwoofers are the worst hifi part to buy new and shiny, massivly overpriced since many people want to feel that BASEEEE but dont know what a good subwoofer actually does. In a subwoofer ther needs to be a driver ( the thing that moves the air ) a GOOD Case for the driver to sit in. Plastic is a no go in any high quality spekaer and is only for 10-30€/$ speakers. Your best bet is to go for a Wood Case, make sure to check the thiccness. A subwoofer Case needs to be sturdy for the driver to play good because vibrations potentially destroy your sound quality. A subwoofer that plays directly to the ground CAN be fine, but you need a very solid floor. its better to have the subwoofer play into the room from my expierience. The place where a subwoofer needs to be is mostly underrated. The subwoofer needs a good place to play nicely like every other speaker but its true that its harder to tell where the subwoofer is from only listening. The deeper frequency the harder it becomes. Sub Range normally is 80hz down to whatever he actually can do. Most subwoofers stop playing at like ~35-40hz which is great for music but not low enough for a really cinematic movie expierience.
The bigger the membran that moves the air potentially the deeper the subwoofer can play, how much this membran can move forward and backward is important as well. So what volume of Air the Subwoofer can move.
A nice trick to find out where to put your subwoofer is to place your subwoofer into your listening position and then play some base heavy stuff. Crawl around the the Floor, whereever you got a good listening expierience, place the subwoofer at that place. make sure to check diffrent angles the woofer plays. a bit to the left a bit to the right etc. also this is not a 100% perfect solution. If not statisfied dont deny your expierience, try another position. Most subwoofers i encountered in a living room did pretty much nothing to the expierience, make sure you use your investment the right way. Decent Speakers that stand are usually enough for Music depending on the size of the speakers ( drivers ) and the size of your room.
In every situation your speaker setup is only one half of your listening expierience, sound is extremly dependent on the room your actually playing Music. The harder the material the sound touches, the more it reflects sound. The softer the more it absorbs. In 95%+ of living rooms you got too much reflection and not enough absorption. While Absorber work pretty well, they take alot of place and may not fit the look of your room. But in a living room there are also alot of things that absorb sound, your couch for example probably absorbs pretty well Curtains as well. Maybe a carpet not only where you sit but to your TV and to your speakers as well. Critical palces to check for a bit of absorption would be the first reflection places. To find out where they are have someone move a mirror around near the walls, while you sit in your listening expierience. When you can see the drivers in your speakers you get direct reflection to your head. If possible try to get some soft materials to block those first reflections. A living room needs to be a place where you enjoy being. so dont overdo it but also consider how much nicer talking becomes in a room that has less echo. This is also quality in a room that many dont consider. For a general rule, the thiccer the absorption Material the more of the frequency curve you actually cover. That means a Curtain blocks high pitch noises but mid or low frequencies are not absorbed at all. Thats why a couch is such a great thing in a living room. You want around 40cm of thiccness for good base absorption. Not really possible but just as an informer... yeah if some of you guys want some advice, im no expert but im invested into this hobby for quite some time. If you provide me pictures or give me a layout of the room im happy to look into it to maybe help with something i picked up over the years. Im not good in telling you what speakers to buy. While its true that diffrent people enjoy diffrent speakers, pretty much everyone enjoys "better" speakers. There is alot of crap which i also buyed and spent money on. Nowadays i build speakers myself which resulted in actually hating all the Speaker companies since generally you get so shitty quality. In Germany we have Teufel and Bose which are the worst offenders, but you can generally go with "the more ad money they use, the worse their product are"