Caps as high-pass filters

If you just use one capacitor the slope will be 6dB/octave.
IMHO, a lousy idea.

Adjusting the filter between sub and speakers can make small differences and improve the match. Most DSP amps will allow you to do this. (Filter slopes are typically between 24 db/octave and 12 db/octave.)

However, adding a capacitor in order to minimize the signal path does not seem like a justifiable reason for making this kind of adjustment.

Lousy huh?
O.K.

Just an idea. Apparently a bad one.

I think the worst result of passive high-pass filtering is the audibility of the HUGE cap one has to use. If one solves F = 159155/RC for 50 Hz and 8 Ohms, one gets 398µF. Do YOU know of a high-quality 400F cap? I don't. Then, ALL the music reproduced by that speaker will be be going thru that cap, so it MUST be very high in quality or you'll hear the negative effects of it. I removed the inexpensive 470µF high-pass filter from my Eminent Technology 8s because they sounded bad enough for even this tin-eared audiofool to hear.

Active filtering, ie before the amp, is MUCH easier to implement (with a small, great-sounding cap soldered into the amp) and better sounding.
.

Line-level then?
Has anyone tried something like this:
http://www.audioc.com/accessories1/misc/hipass.htm

?