What must be done to use the Subgroups for submixing and/or grouping on either console?

To effectively utilize the Subgroups for submixing and/or grouping on a console, assigning channels to the Groups is essential. This process involves designating specific audio channels to feed into the subgroup, allowing those signals to be controlled and processed as a collective unit. By routing multiple channels to a subgroup, sound engineers can mix them with a single fader, apply processing effects, and manage their output cohesively. This approach streamlines the mixing process, especially in complex productions involving numerous audio sources.

While other options may relate to certain aspects of mixing and processing, they do not specifically address the primary requirement for utilizing subgroups. For instance, patching compressors is a matter of signal processing that does not inherently involve grouping channels. Routing through main outputs pertains to the final output stage rather than the setup necessary for submixing. Engaging aux sends is relevant for creating monitor mixes or effects paths, but it does not fulfill the specific need to assign channels to groups for effective submixing. Thus, assigning channels to the groups serves as the foundational step for using subgroups appropriately in a mixing console setup.