For replacement of the IOAudioFamily type kexts for CoreAudio drivers, you want to look at implementing an AudioServerPlugin CoreAudio driver. For a virtual device, everything you need is there. For a HW device, it will also depend on whether or not DriverKit supports the HW. See https://developer.apple.com/library/archive/samplecode/AudioDriverExamples/Introduction/Intro.html https://developer.apple.com/library/archive/qa/qa1811/_index.html https://developer.apple.com/forums/thread/122517 and Google search for "AudioServerPlugin" for other sources of details.

It appears that this workaround is no longer working in 12.1 (perhaps other versions of macOS). If i run this code, with en7 as an external Apple TB GbE adapter, I get the following output: starting with fe80::1016:f5f0:a202:9ee3%en7… [lo0] So the interface being attached to is the lo0 (loopback) rather than the en7 interface. So how do we reliably get the NWInterface on current OSes; as with the OP I need this to open a custom ethernet protocol on a local link with no Internet connectivity. Since kexts are just about gone, we need a mechanism that works reliably in UserSpace to do raw enet packets; this was the path that was recommend (NWEthernetChannel), but there is still not a complete replacement for the KPIs (nor does there appear to be reliable workarounds) after at least 4 years of filing bugs, talking to DTS and the Network engineering team. FB7665061 (April 2020)