Dear Mattkhan, many many thanks for your patience, but something escape me. In order to calculate the flight time (and therefore the phase) of a signal from a single driver to the mic at the listening position I need for a dual channel measurement (FFT). Therefore in the preference of REW I must indicate "use loopaback as timing reference" under preferences > Analysis > impulse response calculation, right? I have tried to put into practice the advices of your previous post (but without using the mix app, CueMix) as follows. Firstly, I have routed "ASIO line in" toward channel 7 of my audio interface and in REW I have indicated as output the channel 5. With a cable I have linked output 5 (REW) with input 7 (JRiver Asio line in).
In this way the signal enter into JRiver and its DSP correctly (convolver with FIR filters for XO, Parametric equalizer) arriving to all left channels outputs (1,3,5,7). Then I have looped back output channel 3 with a cable to input channel 3.
My question is: which channel must I indicate as "Timing Reference output" and "Loopback input" in the REW window "Soundcard"? I have made several attempts, but all unsuccessfully.
May I have a drawing with a graphical diagram of the connections you have conceived? Probably my English is not good enough to understand all you mean.