[GMB]

The audio folks have a lot of folklore but there can be a grain of truth in there sometimes...

One thing to check is that some types of capacitors have a capacitance that varies with applied voltage thus making them non-linear. In many applications this doesn't matter but I see why it might in an LS cross-over network.

Of course the non-polar electrolytics will do that too because the dielectric film is slightly formed and destroyed over a cycle so you can get the effect that a "perfect" capacitor could make it sound different, not just because of different ESR.