can subwoofers make things worse?

I have two SVS micro subs, one sitting beside each of my powered monitors. It sounds well integrated and tight. The room (open floor plan) is 16’ x 24’ with openings all around. 
 

I’m probably a minority here, but I don’t want to see my stereo, at all. If I could buy an invisible stereo I would. So, not that the micros miss anything, but they are as big as I want in the room, and it’s a close call with them. 
 

The phone app is very useful, fyi, and two subs seem much easier to integrate compared to a single sub. SVS has a pretty good shipping and return policy if you are tempted to give it a whirl.  Check out the website. 
 

Hope this helps, best of luck with it!

Yes it sure can if the sub is not time aligned/in phase. I strongly recommend highpassing the speakers (cutting the bass of the mains) through an active crossover as the timing can be corrected. 
 

those small subs don’t play loud and deep. They tend to cut the low bass when pushed hard with digital perfection circuits. Erin’s Audo corner has measurements of a bunch of them on YouTube and probably his website too. Worth watching before you buy. If you have the physical room a good 12” is the way to go was they can always be turned down. 

It's all about what you want.

I believe the REL and the SVS offer easy to return trial periods. One is a sub-bass speaker and the other is a subwoofer. Get both of them at the same time and do your own side by side comparison. It's said they both offer useful phone setup support.

With its dramatic frequency roll off the REL is easily more forgiving of placement at the cost of articulately deeper frequency heft and air. ....Set it and forget it.

If the SVS is properly positioned within your room the flexibility of the remote controlled application adjustments will provide smoother speaker integration, EQ presets and volume control all from your listening position. ....Fun.

All the best with your search.    

The SVS SB1000 Pro would be a better choice than the 3000 Micro and isn’t all that much bigger, goes lower, and is $300 cheaper.  Just another option to consider.

Music or movies (or both)?

Big room or small room?

Neighbors?

The first two factors will depend on what you want and how competently you can work / trial your way through implementation.

The third factor, sub(s) will never make things better! 😉