
Kevin: It comes down to a few things.
As always, first is cost. I’ve picked up a slew of the Audyns on ebay for little coin over the years.
I do have larger values (up to 100 mfd), but they are too big to fit in the cases whereas paired smaller values do fit.
As I said, I’ve been through countless iterations and in one go-round I used the 441P 10 mfd conjugate cap on the 2241 because I had it handy. These are vintage and I got the 10 mfds from my neighbor (a retired NASA engineer now passed), and I could instantly hear a difference. I liked it so I went on-line and was able to find the 441P in 15 mfd and the 3 mfd so these replaced the Audyns.
As for resistors, R1 is replicated because I want the total load to be 28.1 mfd, and this is not a readily available value and two 56.2s split the load so they can handle the wattage.
BTW, it is really not so simple and there are probably no/few other crossovers that work quite like this.
The Heil does not play nice with the 2251 and these require fairly substantial slopes to avoid crosstalk.
To increase the slope on the 2251, I "over-capacitate" it. This then creates a very steep slope, but also a hump just below the slope. The hump falls in the critical area for vocals/detail.
Sound going to the 2251 goes through a choke as part of a second order crossover. But the signal also by-passes the choke (R2/R4/VR1) and this is not in phase with the hump. So the more that is allowed to pass, the flatter the hump becomes, but the steep crossover slope is retained. On the 30 ohm resistor, the system is flattest. As resistance is added through VR1, (starts at ~31 ohms when paired with the 20 ohm series resistor), more of the hump comes through bringing out the vocal range. This pair can go as high as ~52 ohms before going to infinity which removes this portion of the circuit entirely. Note the schematic says "contour" and not volume.
The Heil is treated such that it hits a "brick wall" at the bottom of its range (~2.5KHz) and the addition of the "brilliance" cap does not extend the crossover frequency down, as one would expect, but rather raises the volume in that area just above the crossover frequency, ~3-5KHz increasing detail.