Will I benefit from a subwoofer with 20Hz speakers?

I just re-read that you have measurements and use miniDSP.

Generally speaking to my mind, room correction systems tend to be too bright.  If you have the ability to control the tilt downwards try that.

After you get there, a boost in the bass (below 100 Hz) of around 4 dB is a good thing. The problem is if you aren't flat to begin with. 

Of course, all room correction works best with room treatment.  Take a look at the room simulator, below and see if your measurements are coinciding, and then we can talk about potential fixes.

https://amcoustics.com/tools/amroc

20Hz @ 0 db loss?

"The speaker's published frequency response is 41-20,000Hz. I presume this is achieved in an anechoic chamber. In my room however, it goes down to 20Hz, at least according to the Dirac measurements. In fact, I needed to flatten the curve and  reduce by 5-20 DBs between 20-100Hz due to the room effect."

Nice looking speaker. 

You have a magic room. The speaker defies manufacturers reasonable/real world  low frequency claim? Hmm...

I took a look at the website. This one is over the top:

Here is a photo of my measurements (took me forever to figure out how). 😁

They are taken from the listening position. As you can see, I had to even reduce the low frequencies by quite a bit.