If XT32 subEQ HT cannot solve your problem in the 20-200 Hz, the minidsp has no chance doing it at all. I have my minidsp 2XHD back in the box after spending many hours trying make it work better with and without XT32's help and found it was no possible. The mini can be useful, but in my experience, not when you have just two subs and already have XT32, even more so if you have the Editor App.
Now if you intend to use the mini with Dirac Live, then yes it can potentially do a better job, though it is hard to say.., like what is better? Both can flatten the response, not just on axis, but within the listening window/bubble, in my trail, Dirac did seem to do a slightly "better" job on the impulse response based on my REW plots.
To use the mini with Dirac it would cost another $200, approximately, and only for two channels.