Yes! suomynona is correct.
The minimum signal chain in a modular setup is
sound source -> output module.
That is a the most general (or abstract) signal chain.
A more specific and typical signal chain is
sound source -> VCA -> output module.
This assumes you have a method of turning the volume up and down on the VCA. You could physically turn knobs on a VCA and create some pretty cool stuff. But you will never be able to "turn" the knob as fast as voltage can. That is where the VC part of VCA comes in. For this you need an envelope generator (EG) such as Make Noise MATHS or Erica Synths Black EG/LFO module. Then there is the new Rossum Control Forge with which you can design arbitrarily complex envelopes. And the term envelope as used here can be confusing because even another oscillator can be used to generate envelopes to VCA to open the volume up and close it down. The Mother-32 gives you access to its EG which you can patch in and out, I believe.
Here is a more specific signal chain I used recently in a patch with modules I have
Erica Synths (ES) Black VCO -> Make Noise (MN) Optomix -> MN Erbe-verb -> ES Black Output.
The Optomix was being opened and closed in weird and funky ways using a Synthesis Technologies E350 (Morphing Terrarium). Also, I was using Rossum Control Forge to move around in the wave tables on the E350 which was continually altering the way the MN Optomix opened and closed. Now that I think about it I was sending ES Pico VCO into the second channel on MN Optomix. The same envelope was being used to open and close both channels on the Optomix.
The point here is that modules such as Optomix are mixers which is what you want. The output from your mixer goes to your output module which provides a line level signal to the rest of your outboard equipment to interface with your DAW and keyboards and such. The ES Black Output module is also a mixer as well as an output module.
Taking a signal directly out of a modular system can be done but it will be too hot for most audio equipment which is expecting a line level signal voltage (anyone know what the limits are of line level voltage?).
I hope this helps.