FYI at least in California a manufacaturer must be given a "reasonable opportunity" to attempt to repair the defect (which you have given Mesa) and then must either replace the defective unit if the problem persists or give you a full refund. You bought a particular speaker with a particular speaker configuration to produce a certain sound. That's not what you have. Time to request a replacement and/or a refund (be sure to ask kindly but be firm -- I've learned the hard way that getting belligerent just puts out negative energy and does no good anyway). You paid good money, and for Mesa to tell you that replacing the speakers with speakers that don't sound as good is "all they can do" is absolutely ridiculous.