The model 5 filters are the way to go if you want absolute transparency. However, after I've said that, you can build some that are very, very close.
Most of the caps discussed above have their virtues. Each is a little different flavor. I wish I could decide what was accurate. I sorta favor the Auricaps but as Maxgain says, the Dynamicaps are good BUT they are fragile. I have found Kimber Kaps to be decent along with Hovlands. The Hovlands give you a smooth and warm sound. Pretty much the opposite of the Inifinicap.
When I used McCormack amps way back when, I would solder the cap inside the amp and do away with the extra connectors. The center conductor wire from the RCA input was removed and the cap inserted. Kinda of hard to do that with a lot of connectors soldered directly to the boards now.
Maxgain has the info above for making these. He's right on the money and they are simple to make. I tried the "Nude" approach and actually thought it was better also.
One other note, I was told that the new model 5a's crossover at 100hz instead of 80.
I found using a frequency crossover point just below 80 works best in my room(actually about 73)
Most of these caps are + or - 10%. Auricaps can be specified at precise values at + or - 1% with a given value on special order.
The bottom line here is you really need to experiment. The M-5 filter simplifies this greatly and by the time you get through playing around with the x-2 clones, you could buy a pair of the 5's!
One last note, be careful about the manufacturers stated input impedance. This generally varies a good bit. That's why it's important to narrow your choice down through experimentation.
