There might be more to the "impedance matching" than is obvious. A lot of amps have a DC block capacitor at their input, which attenuates low frequencies with a starting frequency that varies inversely with the driving impedance. IOW, with a high driving impedance, the blocking capacitor lets more ultra-low stuff through (which might be good or bad depending.... some amps and speakers need to keep that stuff out).
I use a series cap as a first-order highpass filter to cross to a sub, and a 'passive' box would move the crossover point all over the place.
I use a series cap as a first-order highpass filter to cross to a sub, and a 'passive' box would move the crossover point all over the place.