Hello! I have just been to my parents' home and I am able to provide proper feedback.
I attempted to install "Slot 249, IOS base 57, d2x v10 r52" and "Slot 250, IOS base 56, d2x v10 r52" from ModMii as suggested. I followed the step-by-step tutorial for ModMii on on the cIOSX rev21d2x: Yet...