Modifying Crossovers

It is fairly well known that even in expensive speakers, there are crossover components that are not the best quality, usually because the company that is making the speaker is trying to keep a good profit margin. It is then tempting for an owner to see what improvements might be gained by swapping them out for better parts. On the other hand, a lot of owners don't do it because the warranty could be voided, and also if they try to resell them, the buyer won't want speakers that have been modified in any way.

Another explanation is that some people have an insatiable urge to "customize" their gear. This makes it unique to them. 

To get a crossover with high end components you'll have to spend $100k or more.  I am currently building new external crossovers for my speakers.  I spent $2300 on caps, resistors, and inductors.   Here is a photo of the final layout completed just last night.

https://photos.app.goo.gl/5maaKbDKvpNdjGja9

There is no way I would mess with factory Crossover of New Speaker, UNLESS many people documented the OEM made a mistake and problems resulted. 

The crossover looks like simple design nice quality to me

https://audiogroupdenmark.com/product/boerresen-x3/

OLD Speakers, I would have my friend check the crossover for out of spec parts, replace them with the idea or restoring 'original', not 'let's upgrade them".

He has two pairs of JSE Model IIs. restored one pair's few out of spec parts. 'Upgraded the heck out of the other pair. We both prefer the simply restored pair to the upgraded pair.

It's very hard to deny the bias of it's better right! he's like me: not necessarily so.

Vintage parts might have been +/- 5%; newer ones, same values are probably tighter specs, say +/- 2%, not going to improve the sound, just typical modern production.