I have done live measurements with REW. I have only compared the frequency response of the loopback through REW vs just using REW directly and it is identical. I didn't check the phase or anything else. I plan to measure some stuff in the next week or two so I will compare measurements more closely between with or without JRiver in the playback chain. I wouldn't be able to check for delay, but it shouldn't matter anyway since you can change the latency of ASIO hardware to vary the delay with no problems during playback.
Ill likely try some measurements tomorrow...
Just now I confirmed I get a good signal from REW through MC in loopback (no stutters, clicks, pops). MC Playback Options is setto WASPI Eventstyle with hardware buffer at anything from 10-100 ms to my firewire Mytek 8x192 DAC. If I use ASIO instead of WASPI I get stutter. I assume I should use the least possible buffer, or does it matter?
Correct me if I'm wrong, but I also assume it doesn't matter what sound device should be set to default for REW to play on (to be looped back to MC).
Do you know REW well enough to suggest what graph I should inspect to determine of Im getting any additional delay, phase shifts, etc from loopback that harms by before/after comparison?
Also, do you know why most have said we can only use REW RTA, not MC loopback, to inspect before vs after results?? It seems to me the way to do it is via MC loopback, unless there are issues that arent apparent.
PS: Since I posted this elsewhere, Ill report these findings there as well..
Thanks