Just in case anybody is still interested in upgrading the crossover parts,
GR Research sells very high quality capacitors and inductors. WARNING: These tend to be physically much bigger than the "ordinary" factory parts. You will need to replace the circuit board altogether in order to accommodate them.
Incidentally, the calculator linked above is essentially useless. Modern crossover circuits are computer-designed by taking the dynamic impedance characteristics of the drivers per se into consideration. The "textbook" (Linkwitz or whatever) filters rarely work properly, without LOTS of trial-and-error. There are a number of Wintel-based crossover design software available for serious DIY'ers.
So, if anyone is interested in "upgrading" the crossover without wrecking havoc to the speaker, I would recommend simply substitute each L/C/R part with a "better" one with the identical value. WARNING: As people repeatedly stated above, this will unlikely "improve" the sonic quality of the speaker at all. If it were me, I would build the speakers from scratch rather than wasting my time and money on the dubious crossover upgrades.
