Hmmm... I'm not sure on this one.

You've got an analog input in both cases, with the mode set to bypass in both cases, with the volume set to the same position in both cases, and the only difference was whether the fronts were set to "large" or "small"? The fact that changing the crossover point didn't affect the outputs suggests that there really is no crossover being applied, assuming that at least one crossover chosen was below one or both of these frequencies. I'd be curious to know what is happening when the frequency is something well above the bass management/subwoofer domain (maybe 500Hz or 1,000Hz), just to see if the ~4dB difference is happening across the board or if it is limited to the range in which a subwoofer would also contribute.