I have to agree with those that have said 3 subs appear to be overkill for your room. I'm completely happy with my 2 Hsu in a listening space much the same as yours, 12x20' but it's open floor plan is wide open to another area comprising to at least 2x the square footage. Also remember that Audyssey will only correct for timing and FR on 2 subs individually. I'm not sure of the capabilities of Dirac 2 but Dirac 1 could only correct for one sub.
As you go up the chain in the better room correction systems the setup becomes increasing difficult and time consuming. MHO is that Audyssey when combined with the new Editor app will do a job that most users will deem "good enough". The next step is to get a UMIK2 mic and install REW to your computer and then do actual measurements of what your run of Audyssey produced. Then you can go back in using Editor and tweak the final results to your taste.
DRC is a large field of available systems but in most cases the quality of the result will depend on the amount of time the owner is willing to put into learning and tweaking his available systems program.
Here's another option, a friend and luminary in the audio field Mitch Barnett, who has also written books on the subject,
https://www.amazon.com/dp/B01FURPS40Has started a paid service where he'll walk you through doing a full professional job of room correction using a variety of software.
Here's a link to his website,
https://accuratesound.ca/If you really serious on getting the very best results possible, he's the man to talk to.
More info on Mitch and his service here,
https://www.audiosciencereview.com/...mitch-barnetts-new-calibration-service.10212/