I've just broken down a cocktail build into a portable unit that puts the players next to each other a la a Street Fighter cab. I've gone through and set all my roms to use the stand up cab mode to prevent flipping when it's player 2's turn, but by doing so the emulator ignores the 2nd player controls so, for example, 2 people playing Dig Dug have to use the same joystick, swapping back and forth between turns instead of being able to use their own stick and buttons. Later games like Street Fighter work just fine, but it's the older 80's games that get me frustrated.
I get that they were likely never meant to work like that, but perhaps there's a tweak I'm just not aware of that will let player 1 use joystick 1 and player 2 use joystick 2.
For the record, I've confirmed that both the general input and game specific input settings have the keys/buttons assigned properly.