I can double check for you, but although the mame docs say you can define a bios name, I've never gotten it to work, save the 1 0 thing I mentioned (which works for playchoice and megatech).
Yeah you make a diehard.ini and simply put a "bios 1" or "bios us" or whatever works in the ini and nothing else. Just make sure the ini path in your mame.ini is defined (by default I think the ini folder is commented out).