There’s no single right answer for this because it’ll depend on what you want to do. Assuming you want to treat the PB and Coco as two stereo instruments with separate mixer sends to the reverb, the minimum you would need is two stereo or four mono inputs to the mixer, one mono effects send, and a stereo return via aux return or additional input channel.
Effects sends on a hardware mixer are usually mono, because most effects are mono input. But my digital reverb has a stereo input, you say. Yes but it is (99.9% of the time) summing the input to mono before it processes the sound and then outputting the stereo reverb mixed with the stereo input via the wet/dry or mix controls. Since you will control the dry signal level with the mixer and set your reverb unit to 100% wet, you only need a mono send to the reverb and a stereo return to the mixer.
You could use up one stereo or two mono input channels instead of an aux return for your reverb IF you want to EQ your reverb signal, overdrive it with the preamps, or send it to moar fx (like the Cocoquantus). Otherwise your reverb will just go straight to the mix unprocessed. That’s pretty standard but hey, this is CL talk.
Now, I find the CL stereo output scheme extremely annoying for my way of working. I don’t want things hard panned all the time, and I don’t want the various sounds generated to be pre-mixed before they get to the mixer. I usually have Coco returned to two mono channels so I can process the two cocos separately, or take the banana outs into other banana devices. With PB, I use the 1/8" output in conjunction with the individual banana outputs sent through a format converter to get them to 1/4" and into their own mixer channels or into some other synthesizer/filter/etc. Sometimes I even use 1/8" stereo to 1/4" mono passive mixing cables so my PB or Sidrax stereo out comes out in mono and only takes up one mixer channel. Note that not all PB generators have an individual output.
