Sell it for parts..

Seriously Larry, the speaker[s] are obviously causing you more heartache than they're worth. The Tech couldn't solve the problem and the problem still exists so it leaves you with little resolve except to sell it/them for parts or dump them. The warranty has expired and you had a couple years of good use out of them so maybe it's time to cut the losses and move on. Only next time you may want to go with what you originally intended and get the JBL's or some other set of speakers that are made by companies that deal exclusively or almost exclusively in the manufacture of loudspeakers and/or sound systems. Yamaha dabbles in so many different areas of manufacturing that it is more difficult to produce products of outstanding quality in each and every area on a consistent basis. Sometimes they get it right and sometimes their products are lacking, as in your case.

Products to consider are JBL, Mackie, Peavy, ElectroVoice, Samson, etc., etc. Or you may give Yamaha another go at it but do your research carefully.

Best regards,
Mike