[Otto]

Hi Steve,

Do the soundcard cal first. You do the soundcard cal with no processor in the loop; just a cable from audio out to line in. After that, you should be able to do a loopback measurement and get a flat line.

We generally don't use digital connections because you can't cal your soundcard with the digital out and an analog in. Just use the analog for now; it's plenty accurate enough.

Yes, you will need a single RCA to 1/8" jack. Don't use RCA to mono 1/8". User RCA to stereo 1/8". You will generally go in on the left side of your input; that's the default of REW, so the most commonly used.