The crossover upgrade is sold by an AV123 employee. They retain the same woofer/tweeter crossover frequency and component values while improving the quality of the components with air-core inductors, sonocaps, etc. The stock X-LS components are good, but obviously AV123 can't afford to put $100 worth of parts into the crossover of $200/pair speakers.
Warning - abefroeman!
This is a controversial topic, but it has been my experience, as well as that of many other more experienced DIY speaker builders, that substituting high-priced inductors, capacitors, or resistors has no audible effect in a properly designed crossover. It might be possible to design a different and better crossover, but to substitute crossover parts with higher priced parts of the same electronic value does little if anything.
I would not pay $126 for "upgraded" crossovers that only use parts with the same electronic values but of higher price unless it is clearly demonstrated that they contribute to improved sound from the speakers.
If you are interested, I would be glad to discuss what my preferences are in crossover parts, but that gets away from your original question here.