I've used AU Lab to pipe my microphone input through my headphones, which is apparently how professionals like to record audio (a "monitor" so you can hear how you sound), but I couldn't get used to it

How was the latency when you last tried it? Most outboard audio interfaces (even inexpensive ones like the Focusrite Scarletts with ≤ 2 inputs) have a "direct monitor" feature that is as close to zero-latency as you can reasonably get.

I don’t remember, or have context for how it feels when it’s instant, so I’m a bad tester.

Maybe that’s why I didn’t like it, a tiny bit of latency seems like a killer in that scenario