From what I remember both output the same as chosen in the menu. You can trim the outputs volumes a. Some time ago it had been posted that the main xlr outs were sweeter sounding (if that makes any sense)That could be some phase reversal in a gain stage of some sort. I have not tried setting the levels of each output {guitar amp on front compared to xlr on rear)to a/b them but I want to not wear out the xlr on the rear. A rigid patch bay would fix that.