Wow and WOW!
As we say in Texas, I feel lower than a snake's belly in a wagon wheel rut. I'm not going to ask any more embarrassing questions.
Moral of the story: Leave it on Low Gain unless you're unable to achieve the SPL you desire (even with the stepped attenuator turned fully clockwise for no attenuation), then bump the Gain up to Medium...
Thanks again to both of you!
(Listening to It's Such a Happy Day, from Jackie Gleason's Return To Me)