This is a separate message from the request for help in a post nearby. I've had the Scarlett 18i6 for a while but had never tried something, and tried it successfully tonight.
Just thought I'd share the technique. In the some versions of Focusrite MixControl I believe for some other models there's a routing preset for "loopback" which allows you to feed your computer sound back into the mix flow and presumably record it. That option is not there in the Scarlett MixControl as far as I can tell.
Someone can inform me if there actually is a routing path for it.
The purpose I had is that tonight I had a bunch of external midi sound modules on a particular piece I'm working on and I was in a hurry, and hadn't yet captured the external midi tracks down to audio wave files.
My drummer wanted to take away the piece to practice against, and I didn't feel inclined or have the time to capture all the external midi tracks as audio when several of the midi tracks are still a bunch of scratch takes. Everything sounds great through headphones and monitoring, I just didn't have the audio/wave files of the midi stuff to export through Sonar as a song.
The technique I used was to take one of the Scarlett stereo outs and route it back in through the back with an actual stereo cable as one of the 18 inputs. I then muted in Scarlett MixControl in the MixControl for that particular input set of channels.
However, in Sonar I created a new stereo audio track and selected that pair of input tracks for the input signal. I armed the audio track and set it to record, and played back the song just as I would listen through headphones.
When it was done I had the mix on the audio track. I was then able to export that mix track from Sonar as an mp3 file.
It was a fast and dirty solution and now frees me up to have quick draft mixes when I have external midi involved and I haven't yet saved the midi down to audio tracks for proper mixing and applying effects, etc.
Probably no one needs this, but thought I'd pass it along just in case you have a Scarlett and had been stumped on how to capture live playing audio from Sonar back into Sonar as a mix track.