Yeah, if the other emus are remappable like mame, I'd do what Miguelsluma said. If they aren't, well, you pretty much have to change ipac.
Mame's (and mess's) defaults map is in the source (
online file with the info). Not the cleanest list, though; might be easier to read by just starting mame and tabbing into "Input (general)" and browsing that. Not sure about the other emus.
Note that mame doesn't have default keys for player2 buttons 5 & 6, and none of the buttons for players 3 & 4. You'll have to remap these in mame if you have them on your CP. Just so you know you're remapping mame a bit anyway you do it.
Also, I suggest looking into
ctrlr files for mame, if you want special remaps for different games, and want slightly better cross version compatibility and more mame crash corruption protection. Might be a little more than you need, though.