The Nord Stage 2 has four audio outputs as shown here: You can send the various sections (synth engines) of the Stage 2 to the different outputs. This allows for more control over the mix and EQ at your output whether it be a recording bus, personal monitor, or live sound board. It’s a rather simple process. Shift -> System Use Program Page buttons to go to Synth Outputs Scroll to change to the desired output
Having over 12 years of keyboarding experience I’ve played on numerous boards and have come to realize the various differences and nuances between the types. There are formal definitions out there and this list is probably not exhaustive, but it reflects my personal opinion. If you are reading this and are unfamiliar with keyboards this is a good place to start. Midi controllers: Make no sounds on their own. Plug them into another device such as a keyboard or laptop to generate sounds.