A link to why stereo, gradient bass (cardioid/dipole) is ideal for (stereo) music in acoustically small, domestic listening rooms. Or why the popular fashion of multi-subs in mono is a poor choice for music.
Use of a mono signal, replayed via multiple subwoofers with suitable signal processing, allows one to present more uniform bass over a listening area.
However there is still no opportunity to present spatial information. Use of two subwoofers placed to the left and right of the listener and playing left and right LF signals allows presentation of spatial information.