"...loopback from output to input on the computer"

There are a huge number of devices available which allow that, also channeling music from your computer audio output (or from about any other source) into an external CD recorder. eBay has all sorts of them listed, but I have never used any and so can't comment on which ones work the best. I do have some device which you can plug into a vinyl disc player to digitize and record the analog signal through a computer, but never got around to using it.