I currently use the mixer that was provided with the Moog Sound Studio (4 mono or 2 stereo), but I was planning on doing some in-rack mixing too (using the VCA Out on the Moog to get modular level). Why are 1/4 cables "the way to go"?

-- blaaank

I'm speaking of a non-modular, external mixer. Those are generally 1/4 inch cables (as are pedals, but you don't seem
interested in those, fair enough). For this simple example, 8 direct 1/4 inch inputs from all or any of your semi-modular Moog family can be mixed in with any 1/4 outputs from your separate modular racks (provided by the Intellijel or similar I/O).

https://www.sweetwater.com/store/detail/Mix8--mackie-mix8-8-channel-compact-mixer

Fairly cheap but powerful, especially if you are recording. I don't use DAWS, just Reaper through a Scarlet Focusrite to record off my mixer into the computer. Well, I did, but I upgraded my mixer so that it can go directly into a USB of my computer without
the Focusrite. Always an evolution. . . .

For about the same price, two studio monitors could easily be attached to the mixer, as well. Not sure how you listen to your patching?