need to record Discord under W10

If you really want to use Discord - or indeed any app like that - then ideally you'll need something like Virtual Audio Cable to extract the stream and send it to Audition, although it's notoriously difficult to set up. Audition uses at its heart an ASIO-based engine which means that it can only use a single interface at a time (that's not an Audition limitation - that's in the original spec), so if your interface cannot access an external stream, then you have to go to rather greater lengths to get things into it. One other possibility is to use the (free) ASIO4ALL driver, which can sometimes reveal other sources and let you feed them directly in - that's probably the first thing you should look at. The basic premise of ASIO4ALL is that it makes Audition's ASIO engine appear like any other WIndows app, altthough there's a latency penalty, inevitably. With speech this generally doesn't matter though.