I've gotten good results using a 3.5mm to RCA cable from amazon plugged directly into my preamp. I've also gotten good results using Airplay from the laptop to my DAC. If your DAC doesn't have such connectivity, try bluetooth as well, and if that fails, definitely try playing the file through Roon. You need to create a file first in REW, add it to Roon, then in the measure tab, select Playback > From File, so REW knows what it's measuring.
REW has a steep learning curve which requires a lot of time/effort, trial/error, but it's worth it. Look into creating Convolution filters which work seamlessly in Roon.