I already made the first IEM's:
2800: 0.1µF in series - coupled in antiphase - 680 Ohm damper - 2mm ID 25mm length
2356: 47 Ohm resistor and 4.7µF in series - coupled in antiphase - 1000Ohm damper - 2mm ID 12mm length
3300: 15 Ohm resistor in series - Normal coupling - 4700Ohm damper - 2mm ID 25mm length
The fitting was now perfect because I used too big tubes and made the molds bigger than my ear canal. So they are not comfortable to wear. Nevertheless I was able to make listening test.
The was a bit lack of bass for my taste. The mid low bass was good and tight but not very much very low bass. The mids were very good together with highs. They sound a bit like the 2356 alone and the 2800 gave a little extra in the highs, but could have been more. Overall the sound is on the warm side.
I also did a measurement on them, and the low frequencies were very flat and not U shaped. I the next ones I will put a smaller electrical resistor and more sound damping to get a slope at the lows. For the highs I will try to get a little more output from 2800 to the overall sound. It might means damping the 2356.
What do you mean 4700Ohm is too much? I found it to be too little. Besides the sound dampers only work for High frequencies. Put the 3300 in series? Why?