i have the same chip, just make a 1 MB bios file with 2x512 bios and switch one will boot the first 512, switch two will bot the second. I use x2 bios manager to do this. Example: I made a 1MB Bios file, first 2 are M7 which was 256k (just copied and pasted to put the M7 in both, and the next 2 are just one 512k debug bios)