If you downloaded a file named xbox_bios_complex_4627_best.bin from a random ROM site, here are the likely issues:
: For true 16:9 anamorphic widescreen, you may need to use an EPROM editor to modify settings like 480p and 60Hz within your BIOS/EEPROM setup.
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There was also a legendary (possibly fictional) BIOS called the that circulated on newsgroups like alt.binaries.xbox. Rumors claimed it was a hybrid: part debug BIOS, part retail, part unreleased Microsoft beta.