249 is only a place where you can install something inside.
what's important is the "something" you put inside a slot.
most games work fine with d2x v8 final base 57, or d2x v10 r52 base 57.
the "base 56" is usually installed in the slot 249, but it's not the best IOS.
as long as you could install d2x with base57 somewhere in slot range 230-251, set that slot number in your USB Loader's setting to use it.