The Microbrute is an almost completely analog synthesizer. This means that the analog circuitry (VCO, filter, etc) is controlled directly by the knobs and sliders. These are in fact potentiometers that form part of the circuits themselves, in contrast to hybrid synths where the circuits are digitally controlled and the knobs and sliders are used to set values in the digital circuits that in turn control the voltages in the analog circuits. This direct, physical control of the circuits is actually one of the reasons some people like this synth so much (including myself). Besides, this design is most likely one of the reasons the Microbrute is so inexpensive.
What this means for the Microbrute is that there are no D/A converters that could convert MIDI signals to voltages, with one exception: you can automate filter cutoff by setting the mod wheel to control the filter instead of the LFO depth.
If you buy a MIDI-to-CV converter, you will be able to use that to automate all the parameters that can be controlled via the patch panel.