One thing I forgot to add is if you are running multiple subs you should invest in the Mini DSP 2x4 HD and UMIK-1 microphone.
That way you can get your subs dialed in before you start running REW.
If you are only running one sub then all you need it the UMIK-1 which you can order direct from here - https://www.minidsp.com/
There is a very detailed tutorial on the Home Theater Gurus You Tube channel on setting up multiple subs found here - https://www.youtube.com/watch?v=_A6gPCczhuU&t=1522s