Thanks for the update. I was going to add this, but you were first... ;-) Hopefully this can help.
Definitely, UC Control/Surface is only control, no audio. Audio is USB and therefore computer... Pre/post is a setting for recording, allowing you to record signals with or without processing. It's not Mac specific.
The 44.1/48 kHz question is "decided" by the mixer, not the computer or Capture/DAW. You open UC Control, see the mixer, launch UC Surface, then you go to Settings and under Audio there are all options available. The rack mixers offer 44.1 and 48 kHz as Sample Rate (44.1 was added in April 2018) and if you don't see the two options, there is something wrong with your computer, not the mixer!
Any settings made under Options are kept from the rack mixer, but they should be stored in a project/scene. When you launch Capture, you will see your mixer, the name of it (with a option to select anther interface) and 48 kHz as FIXED sample rate, because the rack mixer is set to 48 kHz.
I am repeating this because this procedure shows immediately if something is wrong somewhere. When the settings of the mixer (UC Control/UC Surface) are how you want them to be, Capture WILL start with exactly these settings. If it doesn't, something is wrong in the computer, which will also affect any other mixer you connect.
Here are two helpful articles from "Techniocal Articles", dealing with connectors and cables. You need to have the right cables and adaptors.
It might be the best to open a ticket and get some help from Support.