I would like to start by saying that I have no experience with the Exakt box for subwoofers.
Through the experience of integrating two A221 subwoofers into my 2.2 passive system with A212, I have experienced some things that you generally don't hear.
The position of the subwoofer in relation to the satellites is anything but arbitrary. When integrating my subwoofers musically, I can hear and evaluate differences in the range of 3 mm when I move the subwoofers parallel to the satellites in depth.
I never succeeded in musically integrating one subwoofer into the system. A second one was needed.
The order of the crossovers of satellite and subwoofer sometimes does not allow both to run in the same phase. In this case it is necessary to invert the phase of the satellites or the subwoofer. Initially, I had inverted the phase of the satellites and operated the subwoofers in phase. I expected a better impulse behaviour of the subwoofers during playback. Obviously, however, this is not so important. Much more important seems to be the impulse with which the beat is set. This is probably done via the tweeter, as the ear obviously reacts more sensitively there. The perception of the bass is subordinated to this. Meanwhile, the satellite plays in correct phase and the subwoofer is inverted in phase.
Using the subwoofer's internal filters to restrict the signal to the satellites has never worked for me. The signal is sent from the power amp directly to the satellites and to the subwoofers. The satellite runs open downwards and the subwoofer is limited in its frequency response upwards.
Further fine-tuning of the subwoofer then requires a lot of patience.
I can't judge to what extent an exact box makes the work of adjustment easier. But I don't think it makes it trivial.
But when you have managed it, this system plays in such a relaxed, easy-going way that it's really fun. Mind you, my A212s and A221s are already over 15 years old and play passively.