In reply to:
Is there any advantage or disadvantage to setting 0=anything other than 75db??
No advantage, really. Your reference level should be the loudness at which you most often listen to music or watch movies. If you're one of the Dennis types who listens at 100dB+ levels, then it wouldn't make sense to calibrate at 75dB or 85dB.
I guess that departs from your original question, though. You don't need to match the 0 point on the volume dial with any specific dB level unless you really find the convenience or being able to know at a glance what the dB level is. Even then, though, setting the volume to -10 or -20dB doens't guarantee that it'll be exactly 10 or 20 dB less than your reference.
