Need to record mic and computer audio

What Audition records is determined entirely by the OS, and that won't let you record a mic alongside of what's streaming from the machine, as it stands. There are two solutions to this; the first is to use Virtual Audio Cable (VAC) to tap into the internal feeds in the machine and record them to a couple of different tracks on Audition. It's a royal pain to set up, but as a system it's very flexible - lets you do all sorts of things that Microsoft would never dream of letting you do. The second is much simpler, and that is to use something like SoundTap to record the stream - you can add a local mic into it, but it's all concatenated into a single stream. It's doing pretty much the same thing that VAC does, only it hides all the setting up, and just gets on with it. And it works fine - I use it. FWIW, I have no connection with the company other than as a satisfied customer. If you can live with the single stream, then that's the obvious answer.

https://www.nch.com.au/soundtap/index.html