Hi Mike,
I had to replace a circuit board in one of my Odyseey's due to a waek panel, less output than the other speaker. At the time, Jim Power had me swap panels from speaker to speaker to see if it was the same.
Sure enough, with the good panel, the speaker still had weak output. Jim said it is usually the circuit board in the back of the speaker, as there are 2 circuit boards per speaker. I swapped in the new circuit board and the problem was solved.
I would suggest getting in touch with ML service department. If you swap panels out , the good speaker panel to the bad speaker, will tell the story. If the speakers plays at full output, you know the panel is bad, if it doesn't play at full output, it's the circuit board.Swapping the panels out took less than 1 hour start to finish.Hopefully , if it is a circuit board that the warranty is still on your speakers as it is quite pricey.
Don't worry about the circuit board swap either, it is quite easy to do also. ML service department should have you up and going in no time.
Goodluck, Greg