Bill,
After much fumbling about, I have (finally!) defeated my long-time nemesis: Serial cable pinout. My specific problem was using 6-7-8 pins when quite surprisingly, only 1-2-6 worked:
1 - A+ (Orange White)
2 - B- (Orange)
6 - Ground (Green)
For my setup, 9600-8-n-1 works well for the 20m cable run from the garage.
Thanks for the support!