Hey Dave - an AFTRS guy huh?
The non-optimized media setting, AFAIK, is to warn you if you are about to import media that uses a codec that is not optimised for FCP. Non optimised codecs will make things very sluggish and painful, so its a Good Thing, unless you enjoy the sensation of growing old while waiting for things to happen on your timeline.
Trim with Sequence Audio allows audio preview of all sequence audio tracks while you're trimming in the Trim Edit window.
Trim with Edit Selection Audio solos the track(s) currently selected in the Timeline for trim edit.
The last two bits of info are cribbed from an article off the web somewhere... somehow .. sometime..