When you apply a filter phase becomes an issue because it introduces phase delay (a type of distortion). But its hard to figure out what's happening without knowing what kind of filter is in the receiver. Or maybe there is something unique about the subs DSP which makes it worthwhile. Very interesting indeed.
If I recall correctly, some filters like the Butterworth ones emphasise even frequency response but introduce big phase shifts while others do the opposite. I guess I've been brainwashed into thinking just use one but it sounds like you may have found that using both solves some unique acoustical issues in your room. Always pays to experiment.
Yes I would like to read that article Jack. Thanks.
