The XB3 uses more then two banks of rom, it bank switchs similar to the MB carts.     Does the 'custom menu' contain any mention of OPA or Micro-Manager, if so it is one of custom POP-Carts we produced under license for Asgard containing the XB3 along with other programs.   I have one of these left in my collection, and plan soon to dump the original rom and grom chips, and release the POP-Cart design and info on 3 PAL's inside at somepoint this year on my site O-P-A.biz   Tomorrow I wil