I use an analogue crossover with 2nd order high pass and 4th order low pass. The 2nd order high pass combines with the natural 2nd order rolloff of the satellite speakers (sealed or with blocked ports).
Aahhh so basically time alignment. OK with you now. Time alignment requires more than xo alignment, the acoustic centres need to be aligned.
This is what I mean by overhang (of the transducer, not the room):
Speaker manufacturers are well aware of this (at least the good ones are) but choose to have reasonable bass extention and efficiency over accurate low frequencies. In order to make this inaccurate bass sound a bit tighter they might even deliberately design 2nd HD into the bass driver.
Techniques like Devialet's SAM (and possibly Linn's, D&D's and Kii's techniques) all improve the time domain response at LF to varying degrees. That's why they sound more "correct".
Of course not everybody likes this "correctness". Indeed, it can be difficult to hear what is better about the sound, because there is something missing (i.e. overhang). However, once you have got used to it, it's easy to hear what ported speakers are adding to the music!