replace Mid-range speaker of Green Mountain Audio Imago VI

Something is causing that buzz...dust cap, loose mounting screw, misplaced wire., etc Can you get at the midrange, remove it, and take a good look for a possible physical cause, or do you think it has voice coil or former damage?

The crossover plays an essential role in what the speakers sound like.  If  you simply replace what you think is a faulty driver with an exact replacement, the crossover inside the speaker should perform as it did with the original, though some break in time for the suspension may be necessary.  Perhaps I'm not fully understanding the question, but before replacing a driver, I'd try switching the drivers between your two speakers and see if the problem follows the alleged faulty driver....should only take a few minutes, and there's no cost.  If the problem follows, it narrows it to the driver.