When I measure each channel I turn off the amps that I am not measuring. The last time I measured with the output of REW directly into my pre/pro input and I measured with the center and subs, then the center without subs and I saw no difference. It was the same for the surrounds. I will check again since I have done this before and I did not see this happen. I noticed when I checked the output of my player with a CD using Pink PN noise I made using REW, that my center channel had lower output around the crossover. It may have been some fluke that I am not sure how I did, so I will recheck.