You are talking the front pulley? If so, that frequency relates to the torsional resonant frequency of the crankshaft. That will relate to its torsional stiffness (this is the typical weakness on an inline 6) relative to its moment of inertia. You have an ignition firing somewhere in the engine three times per revolution, and you have a firing at the front cylinder (furthest from the flywheel) once per two revolutions; there are all manner of sources to excite that torsional vibration at all sorts of multiples of the engine RPM.
The frequency that damper should be best at absorbing, is the frequency near the torsional resonant frequency. This will depend on the torsional stiffness, inertia, etc which are pretty hard for the average backyard mechanic to figure out.
If you are dealing with an unmodified BMW S52 engine then don't modify it and use that damper unmodified, and don't change the flywheel inertia too much, either. Trust BMW's engineering, unless there is strong evidence that you shouldn't.
If you are hacking parts together from different engines or if you are lightening the crankshaft or doing some other modification to the crankshaft or using a lightened flywheel, good luck.