How good is the crossover in your loudspeakers?

There are a few different things going on here. 

1. Most speakers comes crap crossovers. Even with higher end speakers, there are compromises with the crossovers. Any company will skimp on parts for profit. Putting in higher end parts of the same values will give you much better sound. As everything audio, there is a point of diminishing returns. Replacing a $1 cap, with a $20 cap will be a night and day difference. 

2. Danny has his own view of "perfect" sound. His goal is to always have a pan flat response. He tunes everything to get that.

3. Danny's kits re expensive, and offer mid-grade parts. He also rinse and repeats most of his kits. He is the place to purchase "No-rez" dampening, so it's in every kit. Along with his tube connectors for speaker wire.  Again, high priced stuff that is more mid-range. 

4. Yes, some of the stuff he is done, the manufacture has noticed and incorporated some of it in the later design. Why not? They get almost free R&D.

Almost any component we purchase some kind of compromise in it to reach a price point. Most of the time, replacing the lower end part with a higher end part will produce better results. This is why we purchase expensive power cables, speaker cables, etc...

Danny is Danny, at least we learn something from what he is saying, get a better understanding on how speakers work. 

Almost every speaker I have torn into has had cheap, or really cheap crossover parts. Even some more expensive speakers still have crap parts in them. These will sound better with better parts. Even changing the sand cast resistors for higher quality ones will have a affect on sound. 

High quality parts are stupid expensive, and sometimes HUGE. Will a $2000 speaker sounds better with a $2000 crossover? yes, it will, but is it worth it?

With old speakers that caps have drifted, or going bad, just about any cap replacement will sound much better. You can do a full recap on a pair of speaker for under $100 the before/after will be huge! 

Sonic Caps are good, but they are bright, sometimes harsh, can be clinical. Not all vintage speakers respond to these kind of caps well. They can loose their warmth, smoothness. IMHO, I will not use them in the tweeter circuit. They can make good speakers become fatigueing speakers. 

@invalid I'm not saying that they are bad caps, just bright/detailed. 

Have used them in both ribbon and horn speakers, they were too much for them. Think more modern less sensitive speakers will benefit from them, also any speaker on the darker side. Put them in a bright, high sensitivity speaker and they become overwhelming.