General thoughts:
The practice of matching both speaker units and crossover components had merit 30 to 50 years ago, when both speaker units and crossover components were not manufactured with the precision it is done today.
As you can read in this article, such practices are no longer needed.
Speaker units:
When it comes to speaker units specifically, manufacturers like SB Acoustics, Scan-Speak and SEAS now produce products with such small tolerances that matching (pairing) units no longer makes any sense.
In addition to vast improvements in production methods, all leading speaker unit manufacturers now have much better quality control and extremely precise measuring equipment that simply wasn’t available 20 to 50 years ago.
We therefore do not offer to deliver matched (paired) speaker units unless the manufacturer delivers the speaker units already matched (paired).
Crossover components:
Modern crossover components are now produced with such low tolerances that it makes no sense to match (pair) coils, capacitors or resistors.
As an example most wire-wound audio resistors have a tolerance of 1%, most induction coils have tolerances between 2% to 5% and most audio grade capacitors have tolerances between 2% and 5%.
Such low tolerances makes it redundant to match (pair) crossover components, it is a practice carried over from a time where components could not be produced with today’s precision.
How components are matched (paired) and why it is an expensive process:
When matching a pair of components, you have to firstly decide what the tolerance allowance is.
In this example we will use a +/- 1% tolerance for matching (pairing).
As an example we will look at the 4.7 uF Superior Z-Cap that has a tolerance +/- 3% on the nominal capacitance value.
This means that the allowed capacitance value for this capacitor type to be within tolerance will span from 4.56 uF to 4.84 uF (rounded off).
When doing a matched pair the first step is to find two capacitors that are both within +/- 1% on the nominal value, so 4.65 uF to 4.75 uF (rounded off).
Then the capacitors must further be sorted so that the two capacitors that are paired also keep within a +/- 1% tolerance on their measured value.
So, if one capacitor measures 4.65 uF the other one must measure between 4.60 uF and 4.70 uF for the pair to be within +/- 1% tolerance of each other.
This process takes a lot of time and will come with a substantial cost.
For induction coils specifically they are most often produced to order, so to produce matched pairs it come with a lot of material waste to make matched pairs, which is both costly and not very environmentally friendly.
Conclusion:
With modern precision and the quantum leaps that has happened in the production precision and quality control of modern speaker units and crossover components the practice of matching (pairing) speaker units and crossover components no longer makes any sense from a technical, audible, and financial perspective.