Will I benefit from a subwoofer with 20Hz speakers?

My source is a minidsp shd studio with Dirac going into Denafrips Gaia DDC to Denafrips T+ DAC to McIntosh 601 Monoblocks to Cabasse Pacific 3 speakers. 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.

So, considering I already go down to 20Hz, is there anything else 1 or 2 subwoofers will do for my system?  Would it create a more consistent low frequency field? I see many people adding up to 6 subs, so I wonder what I'm missing. 

Thank you for your insight!