Some of the controls - AHDSR envelope, resonant high-pass and low-pass filters - are classic analog synthesizer territory. There is also vibrato and low-pass filter wobble with more parameters than just the basic speed and depth. There are up to five unison voices with adjustable detune and width.
The key to the sound is the voicing. Each cyborg is based on a set of bowed string samples which have been processed into loops with infinite sustain. There are long (more organic) and single-cycle (more synthetic) versions of the loops. The loops are played starting at a random point, and every unison voice is randomized differently, which makes the phase relationships between unison voices unpredictable. Also, rather than use different versions of the same note, the extra unison voices are created by shifting higher notes down, which makes the sound richer and thicker. There's also a humanization LFO, which can be used to add randomness to the vibrato, volume, and other parameters. Its phase is set to a different random value for each unison voice, which can make for very long and evolving textures, as the different voices' vibratos and wobbles drift out of sync. All in all, these are either very organic-sounding synthesizers or really synthy sounds made from real instruments.
Each of the three is somewhat different. Zinc is made from samples of a double bass being bowed hard with a lot of rosin on the bow, has a larger number of source samples which gives the additional ability to select how far the extra unison voices are shifted, and also includes a four-voice noise oscillator made from bow screech samples. Blackheart originated as samples of a cello, has a higher range, and includes a three-voice noise oscillator created by filtering some notes so that only unpitched screech remained. Ironface is made from quieter and warmer double bass samples, and instead of a noise oscillator includes a blendable set of distorted samples.