Both sets of speakers are calibrated to be equal among themselves, but as you have discovered, to listen to each set exactly at the same volume level for testing, requires an adjustment on the volume knob.
Interesting, I thought the auto calibration would set the channel level so the speakers play the same loudness (at the main sitting position) relative to its reference. Therefore when the volume knob is set to 0dB, if calibrated properly I thought a SPL meter would show the same thing for both speakers. That was my understanding, maybe I'm wrong.
