Hi Bibio,
The mike preamp in the Nagra IV-S has a five-position switch for each channel, to set the preamp for microphone types "Dyn 50" (dynamic 50 Ohm), "Dyn 200" (dynamic 200 Ohm), "+12" (condenser +12V phantom power), "+48" (condenser +48V phantom power), "-12V" (condenser -12V Phantom power), and "T" (condenser 12V T-power). Unfortunately you can't use any of these to power your MKH-110, it needs its own power supply which doesn't match any of these standards. But you can send the signal into the mike pre.
It has an input transformer which is switched to set appropriate gain and input impedance for each of these microphone types. "Dyn 50" and "Dyn 200" are, of course, 50 Ohm and 200 Ohm each. Unfortunately the Nagra specs don't mention the input impedance for the condenser settings but an educated guess suggests that it should be fairly close to Sennheiser's specified minimum of 2k, so you should be OK.
It also has an input blocking capacitor that is switched into circuit for all the condenser types "+48", "+12", "-12" and "T", that is 22uF in value.
But you don't want the supply voltages from the Nagra going to your mike so you'll need an external blocking capacitor in line anyway. If you use another 22uF in line, you will have, in effect, 11uF which gives a roll-off below 3Hz. If that sounds too low, don't worry, your Nagra introduces several other roll-offs before the signal ever hits tape.
So, this is my humble suggestion: Send the output from your mike (pin 1) via a 22uF cap to the Nagra mike pre input pin 3. Send the 0V from your mike (pin 2) to the Nagra mike pre input pin 2. Send the earth of your mike (connector shell) to the Nagra mike input pin 1. Switch the mike pre to "T" and you should be well away. If you find the mike is overloading, or is bass light, wire a 1k resistor in series with the Nagra mike input pin 2 or pin 3 and you should be OK.
Usual disclaimer applies. I am not responsible for damage to your Sennheiser, your Nagra, your physical or mental health, your pet or significant other incurred while attempting anything related to the above. But I am confident you should be OK.
Do let us all know how you get on.
With best regards,