Here's a couple of complex crosstalk examples, in this instance with MCM/JCM...

The Toon Brows are a conformer that crosstalks and matches the morphs that deform the figure's mesh to create brow expressions. The figure is mine. The crosstalk also connects to dependencies linked to a ghost bone that drives a control prop that allows direct manipulation of both eyes simultaneously... It controls the brow and eye controllers in the figure, and the lid morphs.

It's the same principle as a simple clothing JCM just a bit more convoluted, and in this instance not via an empty, same principle though. Utilizing an empty in M4 is less invasive and you're not trying to match any pre existing morph in M4, simply drive a morph value in the conformer via a rotation in M4.

The parms crosstalk in the conformer and the target figure...

The conformer Brows...

The Brow expression Parms in the target figure...