After a decent deal of searching, I've come to a few conclusions. Yes, plugging it into the line-in jack would be the simplest way to go about it. I've also considered an inexpensive DAC just for more sounds quality improvements (since my motherboard's a P8Z68-V PRO GEN3, getting old and 'meh' compared to newer tech). But as to options for getting audio from the GPU (after lots of searching, the GTX-1080 does have digital audio output):
Getting a 2-end HDMI (the 1080 only has HDMI and DP ports) connected from the 1080 to a DAC with HDMI input, which in turn connects to the analogs on the Crack. Sounds reasonable? Won't work?