The DCH 148 is one of the hybrid modules that Neumann developed for their transformerless microphones, though it isn't the one in their KM 100 amplifier. In fact I can't find any spare parts list from Neumann that specifies this module, so I don't know what it was developed for exactly. I believe that it includes a DC converter for deriving the capsule polarization voltage as well as the FET impedance converter, the balanced output circuitry and the power supply regulation and filtering needed for this circuitry.
Neumann's hybrid modules were documented in two information files (info0046.pdf and info0062.pdf) which used to be available for download on Neumann's Web site, but have since been taken away from public view. The one which included the DCH 148 (info0046) was dated 2000, and showed eleven different modules with their pin-outs. Info0062, dated 2003, no longer listed the DCH 148 or anything that looks quite like it; quite possibly it has been superseded or discontinued.
Anyway I'd assume that Sonosax obtained some number of these through Neumann at the time, and it certainly makes a lot of sense to use these parts in this application.
--best regards