I would take this sentence and simplify it. In what I imagine it aims to capture, even though the sentence seems specific, the topic is too broad. Applying simultaneous modulation that produces rich sound applies to all types of synthesis and effects.
One approach would be to upload an example of where you’ve “played around with LFOs and envelopes.” Then there is an object in common to speak about. Or, mention a particular goal, like understanding how frequency/phase modulation works, or krell, or is it as simple as wanting to build a classic east coast sythesizer using subtractive techniques you might deploy on a Moog, Dave Smith, or Elektron synthesizer?
Combining Modulation Sources: see above
Techniques for Randomization: I started to locate certain modules on the forum here that were built for this purpose, but they were Audulus 3 versions, rather than 4. Which leads to the point that, right now, most of the action is on the discord channel, in the modules room. Discord
Polyphonic Modulation: Can you share a patch you made of this. This way we skip the possibility of my offending your intelligence by explaining things you already know. It sounds like you have a fairly high level of synthesis knowledge.
Examples of Complex Modulations: audio rate? There is a Reducously Complex Waveform Generator. So in this sense knowing how to produce good sound by utilizing the modulation opportunities that are routed with inputs and attenuators, designed as a module with knobs in mind that provide useful parametric ranges, would be a ‘sophisticated’ subject of conversation as far as I am concerned.
What were you looking for clarification on?