All good,
So if your EMM-6 & S.S. are calibrated and working well with REW, you can use your PC to output either unbalanced RCA or use HDMI or whatever connection that is not high level (amplifed) to your receiver so that REW can send information to the receiver's channels and the sub. If your PC has a DAC that can output line level analog you can use that to send signal to your receiver instead of using HDMI or other digital (though toslink/optical is easy too if your DAC has that output). Your S.S. I think can do this, it's a USB DAC essentially, so REW should be able to send signal to your AVR via the 2x L & R unbalanced outputs on the back of the S.S. at line level. You could plug that into an input on your AVR, like CD in or something, and select that as the input for use to test with. Turn off processing on your AVR and set it to simply stereo or direct or whatever turns off surround DSP/upmixing, etc. And then you'll want to also be ready to tell your AVR that your speakers are large or small and whether or not to use the sub (bass management) or not so that you can control what you're measuring. You may or may not want to turn off any room correction your AVR applied as this will effect signal. So you could measure before (no room correction) and after (with room correction) to see what your room correction actually did.
When you load up REW, instruct it to use your microphone setup and give it the calibration file for the orientation you'll use (straight vs 90 degree). You can get your calibration file from Dayton's website if you don't already have it (it will need to know your serial number for the appropriate calibration file).
You're ready to do some measurements. Load the generator icon and the SPL icon. Set the generator to output "pink noise" and select full range. You can use the SPL meter there to now adjust your SPL until its reference level at the listening position (such as 75db as a common reference level). You're ready to measure. Tell it the range you want to test, such as 20hz to 200hz for your sub, or full range 20hz to 20khz for your mains or whatever. Do that separate or you won't be able to see what your mains and sub are doing individually. This way you can see your room response (especially for low frequencies) and you'll see the drop off of your mains and where your cross over ideally needs to be set. When all done, you can do a full response with your mains and sub to see a summed response in the room. And you could then do the same before/after room correction measurement. You'll find the room correction software of your receiver will do things you may not prefer with your sub.
Very best,
