I think you are a bit too sensitive. Didnt say anything abusive. Indicating someone that he doesn’t understand it. Is not accusing. I know: because Im a teacher. It is an observation. But im not in your world. And you might find it an accusation…
On topic:
As indicated. Usb over audio works fine with big sur in case OB doesnt work. Digitakt can be selected as input. The user in question was talking about Digitakt btw. I also have a lot of outboard gear comnected via usb. And use aggregated devices all the time to combine them. It is the beauty of mac. I also do it for my digitakt and behringer TD3. In windows this cant be done I believe.