there were several different versions of Danner/Eckmiller type of faders. The very early ones that are build of single resistors and the later carbon type ones. Both of them have their charm, I like the resistor type better but the dB range is limited with either 75 or 85dB range, were the carbon type have a 90dB range that is still better than most of the fader out there today.
I saw a few export versions here in the US with 600 Ohm impedance, but as far as I know they were either 200/300 Ohm for european use.
Best way is to use them with IRT specked mixing units like the V75, V2(3)75, etc. than you won't have any level issues. The resistor in front of it will change the frequency response as well the noise level, but if you do not have any other way of doing it... It works to a point.