Many users have difficulties to understand what the 'ports' actually do and how they can be used. The "Control" port is used for controlling the mixer via UC Surface (and QMix) and you can either connect a computer directly to the mixer, or you can connect it to a router, respectively a local network. The direct connection mixer/computer does not allow remote control, so the router/local network solution is probably always the best solution.

"Audio Network" means AVB and everything you connect here MUST be part of the (PreSonus) AVB network. Newer Macs have the AVDECC option for AVB, which allow them to be an 'endpoint' in the AVB network. A Mac has no AVB splitter, so you need to connect mixer to stagebox and stagebox to Mac. If you want to get to know more about AVDECC, check the articles in Knowledge Base (PreSonus website -> Support -> Knowledge Base -> Audio Networking -> AVB - Audio Networking).

AVDECC can replace USB, but USB also has advantages and is much easier to handle. UC Surface and Studio One do work in a network situation, but Capture not, because it will always 'look' for an audio interface to adjust its options accordingly. If there is only a computer available as audio interface, Capture will lose the multitrack option.