This depends on the receiver/processor. Most of them that I have seen don't require you to adjust the volume before calibration. On mine, upon entering the reciever internal test tones the volume is internally auto set to 0 dB. I can manually turn the knob down while the tones are playing to verify this. And as I said before, many offset the level by 10 dB so that you can use a 75dB tone to calibrate to, that is translated to an 85dB level when in use.
Bottom line on calibrating is to go off of your receiver manual as to how the calibration should be done.
Oh, and yes I agree that listening at 0 dB is a bit too loud for me too. I'm usually around -7 dB for movies, and anywhere from -15 to -30 dB for music.
