Original equipment crossover parts are almost always cheesy in "popular" loudspeakers. Always use open, air core inductors and at least Mundorf KFP capacitors. Tweeter should be easy if the price is right on the used speakers you intend to purchase.
KEF "Q"uestion
I am considering a pair of KEF C55 speakers listed on the local CL. I did some research and there appears to be a common issue with tweeter failure linked to the ferrofluid used to cool them (it can harden over time). The speakers are in pristine cosmetic condition, but that's all I know about them at this point. Anyone have any advice or recommendations on this speaker model?