I tried many, many different combinations, as Homer suggested. After
I tried those combinations, I saw Don's response. Based on all the
combinations, I finally concluded that the "Power Line Transmitter"
AND the speakers must be plugged DIRECTLY INTO ELECTRICAL WALL
OUTLETS.

If I plugged the "Power Line Transmitter" into a POWER STRIP (SURGE
PROTECTOR) and the speaker into a DIFFERENT electrical wall outlet
(not the same wall outlet as the surge protector), the speakers did
NOT work. If the speaker was plugged into the wall outlet that
contained the power strip with transmitter, the speakers worked.

I think I have discovered how to make it work properly, thanks to all
your suggestions. My other wireless speaker system works fine but this
one was problematic. I do have a couple questions that are more out
of curiosity:

1) Was the surge protector related to the problem?
2) Does the "power line transmitter" work differently than other
wireless speaker transmitters? (does one type of transmitter send
radio waves and the other type send the signal through the power
lines?

Thanks to all of you for your assistance. I am a heavy electronics
user but I lack technical knowledge of electronics.

Lin