Alfred: (I assume you are a beginner as you are asking where to get wire)
A second thought on my above post. Maybe I was having a bad day. There are some pitfals, as noted, but as Celtic66 noted it is not rocket science and caps really do make a big!!! difference.
I think if more folks understood that they would save all their cable $$$ and start tweaking their speakers. You cannot believe the junk they put in even expensive stuff. Really I think that your instinct is right. Even if you muck it up its a great education.
Anyway-some good sites off top of my head to find needed info and buy parts. Zalytron.com, Speakerbuilding.com, Northcreek.com, Stryke.com. Also check out the Speaker building Network. Also the Decibel Dungeon has some great stuff, if its still there on real basics ..how are your soldering skills? I do not have DD's site anymore but do a search for it and read the whole site before you start surgery.
My suggestion is use Northcreek for parts and if you are going to the trouble get the very best. Stay away from mid priced metallized caps. I hate the typical metallized-film polypro caps like Salons. Use the best Northcreek or Hovland has to offer. Especially important for the tweeter.As Celtic said-keep the same rated caps!!!
I have never doctored a paradigm and it will be hard to know exactly what you are going to get in the end. If you want a real project and have any wood working skills remove the crossover from the box and mount it externally on the back. You can tweak and listen, tweak and listen w/o tearing everything apart.
I didn't mean to write a book here.
PS: Good luck: If you speaker stars smoking it is probably a sign you did someting wrong.
Sincerely, I remain