OMG OMG OMG! WE GOT THIS TO WORK!!!!
Here are the steps I had to go through. Yours may differ slightly--it depends, I believe, on what version of MM is running on your M9.
* Install the Amazon store from here: https://www.amazon.com/gp/mas/blp/install/
* Open MM and click one of the UPGRADE options
* The Amazon Store will launch (note, for me it would not launch if the M9 was connected to my computer--unplugged it, it worked fine).
* Login to the Amazon Store.
* Complete the purchase of MM Pro. It will download and install.
* Here's the bit you may or may not need to do. I had to uninstall MM at this point.
* Open MM Pro, it will say it needs to install MM, and it will offer you the links to do so.
SUCCESS! I have sent MM some money for the software, and I am now running MM Pro on the M9.
THE LONG NATIONAL NIGHTMARE IS OVER.