- XO is a crossover.
- BW Butterworth, LR Linkwitz-Riley, BE Bessel which are types of crossovers. Each type has a different phase and group delay which impact how well the subs integrate with the mains.
- Order is dB/octave and controls the slope.
The Vienna Acoustics Mozart Grand SE claim 30Hz bottom end. It's a ported design. The subs are unported and thus the bottom end characteristics are radically different.
It's a good move to use the miniDSP. Turn the sub's XO frequency all the way up and set Phase to 0.
You should use something other an integrated so you are not driving the main speakers full range. With a 70Hz corner in the miniDSP, I surmise there is a LOT of incoherent bottom and mid-bass in the room. 70Hz is easily localizable.
Having used full range monitors in recording studios and subs at home, it my experience that maximum musical impact occurs with coherent low end.
Good luck.