Mapping 4 Player IPAC controls (keyboard) for use with MAME .271 in BB/LB

[TheDude101010]

I'm changing my arcade cab from a retropi to launchbox/bigbox via PC and am hopelessly lost/confused when trying to map my IPAC4 (keyboard inputs) for use with my MAME library. It seems that the one place I've been able to find a way to enter keyboard inputs is simply to navigate within BB and not at all to do with gameplay. How do I take a fully-mapped IPAC4 (4 joysticks each with a coin and player button as well as 6 other buttons...and a 5th joystick with coin, player, +3 buttons) and map it to play the MAME games? I'm good with editing a file (actually that's preferred) but can do it through the GUI as well. I feel that it can't be far from where I am but I haven't uncovered it yet. Thanks in advance.