I see questions like this a lot and here's my general advice:

Unless you believe you know more about speaker and crossover design than the manufacturer's engineers, you're better off leaving well enough alone. Of all the things one could do to improve the quality of their system, replacing crossover components is near the bottom of the list.

--Ethan

Hi Miles,

Yes, one can easily mess up the sound of a speaker because each capacitor brand has its own sonic signature, which can change the sound by changing the tonal balance, focus etc. Changing the caps can cause tonal variations over a much greater range than 1/3 octave, which the AES has determined as the minimum bandwidth one can perceive. As the bandwidth of change increases, any change becomes more noticeable.

If one changes the caps, other modifications may be necessary to balance the speaker tonal wise. This includes slight changes or additions of resistors to lower one driver, or to flatten the response on one or more drivers.

If the original crossover capacitors are bi-polars, the task becomes even more difficult as bi-polars are really quite poor. Even among polypropylenes or teflons, the terminations, thickness and type of the foil/metalized film (esr) becomes a factor. I would suggest that one really needs to hear a speaker with the changes first before committing to such an expensive cap.

Hope this helps.
Steve