Caps as high-pass filters

I have been very happy using the high-pass filters on my subwoofers to blend the subs with teh speakers. It works well.

However, in an effort to minimize signal paths, wouldn't it be more efficatious to use a capacitor at speaker level to compliment the low-pass filter characteristics of the sub, bypassing the extra couple of meters of interconnect?

Pre=> amp=> speaker level input of sub with lowpass filter
Pre=> amp=> capacitor=> speaker

Anyone try this before?
If so, how would I figure out the capacitor values for a given slope and frequency?
Suggestions of type and brand of cappacitor?

Thanks for any input!