This was great advice! The key thing about Equalizer APO is that it does its processing of the sound before the Windows sound API, so any program recording from my mic gets the processed version, and there's no virtual microphone needed (well, the actual microphone becomes virtualised - there's no separate device). I have that all working, and mostly followed this tutorial: https://www.youtube.com/watch?v=J3fBx2ftaBs

I adjusted the numbers for my setup but his were a good starting point.