There is a very sound mathematical / physical explanation why more small speakers will not work very well (perhaps only with very low power, just like in a headphone).
In order to feed a constant sound power in the air, the excursion of a speaker with a certain surface must decrease its displacement with the square of the frequency. So, low frequencies require very large excursions.
Above the resonance frequency of the speaker the amplitude of the cone is mainly damped by the airforce. This means that the electrical power is converted into sound power or air pressure. Above a certain frequency the mass of the cone will play its role to decrease the amplitude; hence the speaker will have its upper frequency limit.
Below the resonance frequency of the speaker, the movement of the cone is mainly determined by the stiffness added with the air pressure built up in a closed box (so not by the movements of air). The amplitude of the cone will hence be constant at a certain voltage (and supplied power) independent of the frequency. This implies that the air sound pressure diminishes with the square of the frequency below the resonance frequency of the speaker(s).
So, a bunch of small speakers with an eigenfrequency of e.g. 70 Hz will not solve this problem and will never produce e.g. 30 Hz with sufficient sound pressure.
A solution could be, when you use small speakers with very low stiffness and sufficient volume in the box (thus with a low eigenfrequency!); of course either the excursion distance must then be large enough or the supplied power not too big; otherwise the cone will clip to the end of its free moving space.
See for the extended mathematical explanation:
An example of a relative small 8" speaker with low eigenfrequency is the KEF SP1039 with 25 Hz. The modern 8" Visaton WS20 scores worse with 47 Hz.
When I read the above mentioned article I finally understood why the bass in my KEF 104 was degraded so much, when I replaced a dead SP1039 with a the well-fitting WS20. So, finally I bought a used SP1039 to restore the good basses of my KEF 104.