I find this interesting. Four good budget subwoofers vs two good ones that cost the same?
Partly a mathematical exercise, how much air can these two different solutions pump?
We are not that sensitive to distortion in the sub-bass area but on the other hand subwoofers can really produce a lot of distortion. Four subs that help each other, higher sensitivity on the entire 4 sub bass system, each one does not have to exert themselves (distortion) then but then the subwoofer itself must have reasonably good performance (dig as deep as you want, level distortion single sub, FR which is EQ friendly ).So little back and forth to think about.
I'll leave aesthetic aspects there, that is, fill the combined listening room, the living room with many ugly cubes.
In practice, it can of course play a big role in choosing the number of subwoofers you want to fill the living room with.
Tip:
Edit:
Easier with more subwoofers to solve bass problems that MAY arise. Prerequisite for acoustics in the room and subwoofers that can cause problems, that is.