How can I retain volume settings upon plugging in different speakers/headphones? On the rare occasion that I would like to plug in some headphones to my Mac Mini, rather than speakers, I often turn down the volume before plugging them in, because the first "blip" is rather loud, and probably isn't good for my headphones. However, upon plugging them in, the volume will revert to 100%, and I often get an unpleasant pain in the ear because of it. Is there any way to make the volume stay where it was before?
As far as I can tell, the Mac maintains two volume settings: one with headphones connected and another without headphones connected. If the volume is turned down with headphones connected, it should save that setting the next time headphones are connected.

That said, if your concern is that the "blip" is too loud, it can be disabled in System Preferences; under Sound » Sound Effects, deselect Play feedback when volume is changed.