Hello
I am a macOS system software engineer.
I've created USB comm software as well as kernel extensions (network filtering, device drivers and kexts for intercepting devices before they are matched by the system services).
At IOKit level I enumerated, matched with, and interacted with HID, CDC and "bulk"/printer USB devices (from user-mode apps).
My CoreAudio related experience is building low level audio recording code (for network streaming) based on Audio Queues, creating Audio Units (Mac version of VST plugins for DAWs like Logic and MainStage), working with CoreMIDI, DSP algorithms.
A lot of this history is reflected in my past projects here on freelancer.
What kind of device are you building the server plugin for?