The one thing is will the board take buttons at same time or are they through another.
You can connect both your rotary joystick and buttons through the KADE miniArcade 2.0 -- assign any input ports not used by the rotary function to your joystick U/D/L/R microswitches, player buttons, and admin buttons. (Coin, Start, Exit, Pause)
- Start with the pinout for your AVR. (see above) Make a list of which wire you want to go to each input port and what keystroke you want each input port to send.
You may not want to use the MAME default "modifier" keystrokes (Ctrl, Alt, Shift), since some combos can trigger hotkey functions.
- There's a list of unused keys at the bottom of this image that you can use for P1B1, P1B2, and P1B4.
- Also, you'll probably want to change the MAME P1 defaults for rotary from "Z" and "X" to "[" and "]" so they arent the same as P1B5 and P1B6.

LMK if you have any questions that aren't covered clearly in the User Guide.

Scott