With the new extended mode firmware it can handle up to 26 dedicated functions using "impossible keypresses" (Joystick Up and Down at the same time, etc) without the potential problems with shifted functions. (unintended functions triggered)
Can you explain please? How do you use it, and can I use it in MAME ?
The default keystrokes are for MAME, but you can customize them as you see fit using the
KADE Loader program v1.0.9.0.
The specialized "backward" wiring pattern is shown in this diagram -- encoder inputs on the left are connected to the COM (common) tab and ground is connected to the NO (Normally Open) tab.
When the switch isn't pressed, the COM is connected to the NC (Normally Closed) tab which connects to the next switch to the right as does the other inpupt for the combination.
When the U+D switch is pressed, both the Up and Down inputs are connected to ground, the firmware does some math to see if a combo has been triggered, filters out the component (Up and Down) keystrokes, and substitutes the appropriate keystroke for that combo.

There is also a diagram with diodes that shows how to connect 5-pin joysticks (LS-32-01, etc.) and 2-terminal buttons (Goldleaf, Sanwa, Seimitsu) for this firmware.
The nice thing about this firmware is that unlike shifted functions, you don't get an accidental other function because the other player is pressing buttons or moving their joysick while you're coining up or pressing start.

If you still want to do shifted functions, those are still available with this firmware:
20 regular dedicated inputs - 2 joysticks and 12 player buttons
6 "impossible" combinations - U+D, L+R, and U+D+L+R for each player
up to 12 shifted functions using HWB - one for each of the 12 player buttons
Scott