The perspicacious solution was amongst the responses that were kindly sent
to me: check the mixer.  Somehow the analog inputs spontaneously changed to
MUTE.

What I don't understand is why, regardless to which card they were
'tethered', the problem only occurred with SF, but not Audition.

I am ashamed that I don't recall who made that suggestion.  You should be
praised in public!

I didn't get to try re-downloading the drivers because they're apparently
no longer provided by Sony's website.  All I found there was the manual.
A free site that I found seemingly predicated my accepting the drivers
along with a new tool bar & perhaps other 'stuff'.  NO THANKS TO THAT KIND
OF
'BENEFIT'

Gratefully,
Shiffy