Micky (and others, whose replies I've really appreciated!) -
Thanks for sharing your thoughts about this. What a frustrating dilemma to try to solve! As I mentioned in one of my replies, the sink we chose isn't a standard rectangular shape, but has some "free form" modernistic curves in it, so the hole for the sink in the granite countertop was cut to that shape. Woe is me -- to try to find any other sink with that shape and size!
At this point, my wife is in favor of our trying to tolerate the smell. Both of us hate perfumed deodorizers so we'll look into alternatives to the Arm & Hammer odor eliminator that hasn't helped.
Another option at this point, though admittedly not a good one: I don't own an airless paint sprayer, but I may buy or rent one so I can try to spray the Zinsser odor blocker up onto the sides, front, and back of the sink that I couldn't reach well even with the soft foam extension I sewed together. I realize that spraying the Zinsser would be an unlikely help since it didn't block the odor from the bottom of the sink.
If we can't live with the problem, I'll contact granite countertop installers to see if they can lift the granite top and replace the sink (that is, _IF_ I can find another sink that shape!).
And I may contact the sink's manufacturer in writing to see if they can be persuaded to accept responsibility. No one buys an undermount sink that may require tearing out the granite countertop in the future because the sink's sound-deadening material starts off-gassing an intolerable stink.