Is More Better?

I hope you have a subwoofer integration and management tool? cos plopping subs in a room, should help but is ideal to be meticulous as this is physics and not vibes

So yes, two extra subs are more than welcome but you gotta do it right

Just a question of what you want out of your system / what kind of music do you listen to. 

Typically subwoofers are carefully feathered in at the frequency of the main speakers have the bass drop off and just make up for the small volume and lower frequencies. So the optimal output from subwoofers is very very small. Typically when I go into a system with a subwoofer or two, the first thing I have to do is turn them down to like 10% output. Since many folks have them turned up way too much.... if they are too lond it screws up the imaging, hides much of the midrange, and throws off the balance of the music.  If you are looking for high fidelity, it is unlikely more subwoofers are a good use of money... other components could be upgraded. Two, carefully integrated is great... extend the soundstage.,.. more probably not. 

Perhaps you listen to some kind of music like the guys in the cars that you can hear a block away from the bass... or this is for home theater to make depth charges shake the foundation.  Then never mind. 

Unless you're setup is in an aircraft hanger, that's crazy overkill, but you do you.

When I ran Dahlquist DQ10’s with double Dahlquist subwoofo, the placement turned out to be important for the best imaging. Low frequencies are supposed to be non-directional, but I think it matters depending on your crossover point and the steepness of the high filtering. I thought two worked much better than one for integration, but it made for a physically unwieldy system. I simplified my system, getting rid of the subwoofers when I changed speakers, as I found the system more cohesive and imaging better, even though I lost the bottom half octive.

More subs located and setup properly will give you a smoother response. You will also have less distortion. I would recommend a minidsp 2x4 for distance and phase control If you are locating them around the room.