Currently, there has been several successful Alternate Minima Tuning Method installations on different users Builds. The Alternate Tuning Method is very smooth and intuitive, some of the additional (yet unassigned) buttons will be used for future menu functions.
Initially, there was a problem getting the Multiple Buttons to decode correctly on some microprocessor configurations. The problems consisted of slightly different internal analog pull-up resistors contained within the different microprocessor package styles, and a user error in wiring of one of the Minima Builds.
Once found, the simple wiring error was easily fixed.
But, the ATMEGA328P-PU and ATMEGA328-MU packages have slightly different internal pull-up values. Properly decoding seven switches on a single analog pin is very dependant on consistent pull-up resistor values, the way around the difference is to use an external pull-up (47K) and proper analog circuit wiring.
To help with button decode consistency, the analog support pins; AVCC, AREF, and AGND were properly configured to be used with pin 26. Pin 26 is connected to the FN Button in the original Minima circuit, and this pin is where the additional buttons resistor network are added.
The external pull-up is connected between AREF and pin 26, and AVCC is connected to +5V via a simple lowpass filter (see diagram).
The Alternate Minima Tuning Sketch which support Multiple Push Buttons is available at the GitHub. Currently it is "alpha" code, but I will update the URL when it has been "committed" to production.